Pure Gospel (Acts 2:14-40, Jeff Kliewer)

Baptism as Assurance and the Need for a Pure Gospel

Jesus, before you left, you said to us, go into all the world and make disciples of all nations, baptizing them in the name of the Father, Son, and Holy Spirit, and teaching them to obey everything I have commanded you.

And you followed that up with that amazing promise to us that, lo, you are with us even until the end of the age. Reclaim that promise right now, Jesus, that the things that you began to do and to teach, as recorded in the book of Luke, you continue to do and teach through your Spirit in us.

And so right now, Jesus, living Savior, living King, as you're seated at the right hand of the Father, we ask that you would also be here with us by your Spirit. Speak through me words of truth. Help me to get out of the way, Lord, that your word would come forth.

And I pray for each one of us that we would be given ears to hear. God, we pray that our hearts would be set on you, that your word would prevail in this place this morning. You have authority to do this, Jesus,.

And we thank you for that.

We ask that you would open your word to us,.

In Jesus' name, amen.

The waters of baptism do not, in and of themselves, wash away sin in any sense, nor is a person saved in the moment that they are baptized. Rather, salvation is something that happens inwardly by the spiritual baptism, whereby sin is actually removed as a person has come to put their faith in Christ.

But the waters of baptism then, subsequent to that, represent that new life that someone has in Christ, being buried with Christ in baptism and raised to walk in newness of life. By being baptized, a person gains greater assurance in their faith.

They become more certain of the salvation that is theirs on account of Christ. And so baptism is very important. Outward water baptism is very important. Just a short time ago, I believe it was about 10 days ago, I was on my way to my daughter's basketball practice.

And as I was driving there, I got the sense that I should drop her off at practice and come back to this other church to join them in their prayer meeting, because I just felt the need to pray. As I dropped off my daughter with the coach, I left her there and I went to this church, and lo and behold, I sat down in the back section to the right, one chair in from the aisle, and began to pray.

And just a moment later, a young man sat down in the chair that I left open next to the aisle. It turns out that this young man is the same guy who came here to this building in December, asking to know about Jesus Christ.

He had heard, you know, through some preaching about Christ and was not saved, but looked on the internet to find an evangelical church. And he called up and I said, come in and let's talk. We talked for a couple hours and he was born again.

He put his faith in Christ. Well, little did I know that when I sat down in that chair, the same young man was getting baptized that night. He had been seated in that chair, but got up to go to the bathroom, and I sat down in the very chair next to where he'd be.

So that baptism service was a Wednesday night prayer meeting and I happened to be there at that exact hour. I count that as a miracle, because I got to witness him being dunked under the water and coming out.

And the pastor, John, spoke across the congregation. He and I had a conversation in front of everybody. It was really funny. I got to pray for him in that baptism and my faith was encouraged. But I think I know why God did that miracle.

I think he wanted to increase the certainty of this young man. He wanted this man to see a miracle on the day of his baptism, that I would just randomly, by some miracle, show up to be there as part of that.

And he left encouraged by that. So I think it was for the sake of his certainty. Certainty is the issue this morning. I know a man who was baptized, probably the 1960s, at a small Mennonite church in Washington State.

He walked with God for many, many years. And this last week, he was staring death in the face, facing an open-heart surgery, a double bypass. I talked to him before he went in and after he came out. And the look on his face communicated what was in his heart, his spiritual heart.

Certainty. There was not a twinge of fear in his eye. And he said he knew he had a choice. He could trust in God through the surgery, or he could be afraid. And he continued to trust in God. He was joyful, he was laughing, he was talking right until they knocked him out.

And he woke up the same way he went in. Trust in a God who can keep him and who holds his destiny. Certainty. He was baptized as a young man, but then through years of faithfulness, seeing God be faithful to him, that faith was strengthened and certainty grew in his heart.

I also saw certainty in one of our young people. This young guy was saved two years ago at Winter Blast. And back two years later, he stood in front of the entire camp and gave a testimony of how Jesus Christ saved him.

A fifth grader preaching the gospel to more than 100 elementary students. Certainty. It came from baptism, but then through faithful living and holding on to Christ. I was so encouraged by that. The waters of baptism are a blessing.

But think about the water that we drink and the water we use to take a shower, the water that comes out of our tap. That water we expect to be pure. And we are blessed to have physical water available to us at the turn of a tap.

Of course, the story that gained national prominence about a year ago was from Flint, Michigan, that their water was contaminated. The purity of their water had been compromised by some pollutants, some contaminants that got into the water.

Here in America, we don't expect that, but in places like India, if there were a missionary in India and even a drop of water were left on the plate before the food was prepared, that little drop of water could contaminate the food and that person could get deli belly.

A stomach that can't handle the virus that's growing inside. A sickness just from a drop of water. You see, H2O is pure, but within that water can be contaminants and pollutants that make what is good and life-giving actually contaminated and cause as much as death.

The same is true of the gospel. The gospel is pure. The gospel is pure water, and we're going to look to the gospel this morning through Peter's sermon. But recognize that the pure gospel that we find here,.

This original,.

See, this is the first preaching of the gospel. This is the day of Pentecost when Peter, for the first time, stands up and proclaims the crucified and risen Savior. This is the prototype, the original.

But from that time on, contaminants and pollutants have been introduced into the water. And what you find in many churches, unfortunately, that name the name of Christ, there are so many pollutants, so many distortions, contaminants in the purity of the gospel that the thing they offer can actually kill.

Rather than give life.

There's no point now in going into the list of those who bring in these things of sacraments and all different forms of works, righteousness that invade the gospel, or the changing of who the person of Christ is and offer something that's no longer the pure thing.

Let's not spend time there. Rather, let's go into the purity of this original gospel and know it and gain clarity from it, the purity of the gospel. Acts chapter two, verses 14 to 40. I'll read it through for the first part of the sermon, which will take a few minutes, but listen, this is the best part of the sermon.

This is where the word itself tells you what God thinks. And then at the end, Peter is said to, with many other words, explain. That's my part where I jump in with many other words, but don't miss this reading of the word because this is directly from God.

Acts chapter two, verses 14 and following. But Peter, standing with the 11, lifted up his voice and addressed them. Men of Judea and all who dwell in Jerusalem, let this be known to you and give ear to my words.

For these people are not drunk, as you suppose, since it is only the third hour of the day. But this is what was uttered through the prophet Joel. And in the last days it shall be, God declares, that I will pour out my spirit on all flesh and your sons and your daughters shall prophesy and your young men shall see visions and your old men shall dream dreams.

Even on my male servants and female servants, in those days I will pour out my spirit and they shall prophesy. And I will show wonders in the heavens above and signs on the earth below, blood and fire and vapor of smoke.

The sun shall be turned to darkness and the moon to blood before the day of the Lord comes, the great and magnificent day. And it shall come to pass that everyone who calls on the name of the Lord shall be saved.

The Person and Work of Christ

Men of Israel, hear these words. Jesus of Nazareth, a man attested to you by God with mighty works and wonders and signs that God did through him in your midst, as you yourselves know, this Jesus delivered up according to the definite plan and foreknowledge of God.

You crucified and killed by the hands of lawless men. God raised him up, loosing the pangs of death because it was not possible for him to be held by it. For David says concerning him, I saw the Lord always before me, for he is at my right hand that I may not be shaken.

Therefore my heart was glad and my tongue rejoiced. My flesh also will dwell in hope for you will not abandon my soul to Hades or let your Holy One see corruption. You have made known to me the paths of life.

You will make me full of gladness with your presence. Brothers, I may say to you with confidence about the patriarch David, that he both died and was buried and his tomb is with us to this day. Being therefore a prophet and knowing that God had sworn with an oath to him that he would set one of his descendants on his throne, he foresaw and spoke about the resurrection of the Christ that he was not abandoned to Hades nor did his flesh see corruption.

This Jesus God raised up and of that we are all witnesses. Being therefore exalted at the right hand of God and having received from the Father the promise of the Holy Spirit, he has poured out this that you yourselves are seeing and hearing.

For David did not ascend into the heavens, but he himself says, the Lord said to my Lord, sit at my right hand until I make your enemies your footstool. Let all the house of Israel therefore know for certain that God has made him both Lord and Christ, this Jesus whom you crucified.

Now, when they heard this, they were cut to the heart and said to Peter and the rest of the apostles, brothers, what shall we do? And Peter said to them, repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins and you will receive the gift of the Holy Spirit for the promises for you and for your children and for all who are far off, everyone whom the Lord our God calls to himself.

And with many other words, he bore witness and continued to exhort them saying, save yourselves from this crooked generation. Now comes the many other words where Pastor Jeff will go on and on and on.

Notice in verse 14 through 21, Peter stands to address them and what he says has everything to do with what just happened. You can't miss the first 13 verses in order to understand what follows. This miracle of speaking in tongues with understanding that people from Parthia and Media and all Mesopotamia, all over the world, these Jewish people had come to Jerusalem and heard them praising God in their own languages.

That's a miracle. How are they speaking our native dialects when these are Galileans? How do they know? How can they speak? And so they're perplexed. If all we had was a miracle like that, it would leave us perplexed, amazed, wondering what does this mean?

But see, God doesn't leave us perplexed. As you look out at the world and you see the beauty of a rainstorm or a snow storm or a Grand Canyon or a beautiful ocean and a beach, you know there's a God. His eternal power, his divine nature are clearly seen by the things that are made.

There is general revelation that tells us that there's a God and when you see a miracle, it falls into that realm. There has to be a God because something supernatural is happening here that can't be explained by mere laws of nature.

If God left us with general revelation and nothing more, we would be lost in our sin. We would know that there's a God. He has divine power and eternal nature, eternal nature, divine power, according to Romans 1.

But how could we be saved from our sin? We need something more than what we can see with our eyes. Faith comes by hearing and hearing by the word of God. God has not only given all mankind general revelation, but he gives what is called special revelation.

Actually, the kids at camp last week learned about general revelation and special revelation. Special revelation is not just what can be generally seen by all people who look at the world, it's special in the sense that it's spoken word that comes from God, then becomes written word in the Bible.

Peter, standing with the 11, will proclaim. He will lift up his voice and address them. This is special revelation. It's a man named Peter, but he's so filled with the Holy Spirit, he is speaking the very words of God.

Special revelation. Men of Judea and all who dwell in Jerusalem, let this be known to you and give ear to my words. He's not merely expressing an opinion, he's telling them what they need to know. Later, he'll say that you can know this with certainty.

We'll get to that in a minute. But he tells them, give ear to my words. Now what he does is he takes from the Old Testament prophecy in the book of Joel, chapter two, and applies that to what they're seeing and hearing in their midst.

These people are not drunk, as you suppose, it's only the third hour of the day. Okay, they didn't just go out and get drunk. This is what was uttered through the prophet Joel. Now this prophecy that we have from Joel is best understood in two parts.

It's all one prophecy, but the first part is especially being fulfilled at that very moment. You say, wait a minute, who's prophesying? In this context, tongue speaking with understanding is a kind of prophecy.

Since an interpretation is being given, they're able to understand, it's not just lifeless sounds, but there is an interpretation given, it is a kind of prophecy. So in the last days, God declares, I will pour out my spirit on all flesh.

Your sons and your daughters shall prophesy, your young men shall see visions, your old men shall dream dreams, even on my male servants and female servants, in those days, I will pour out my spirit and they shall prophesy.

That's the miracle of Pentecost. Men and women alike. It's the mother of Jesus, Mary, and the other women. It's the 12. It's the 120 believers speaking languages they don't know and declaring the wonders of God.

The second part of this prophecy, I think looks to the end of this age. Something new started at Pentecost, when this miracle began, when the Holy Spirit came as Jesus promised he would. Now, go back to Luke chapter 24.

Jesus says, wait in Jerusalem until I send the promise from my Father. Acts chapter one, this happens. He ascends to heaven. And Acts chapter two, the promise of the Father, the baptism of the Spirit.

The Holy Spirit comes in Acts chapter two. Changes everything. When Jesus Christ came to earth, the world would never be the same, would it? This innocent Son of God, the Messiah has come. He dies on the cross and rises from the dead.

It changes the world. Likewise, when the Holy Spirit comes, everything changes.

The church is born.

A new age has been ushered in. So it's marked by this incredible miracle. And now we look to the end of that time period, this church age. We read about it in the book of Revelation, when the moon is being turned to blood, the sun is being blotted out in darkness.

There's signs, there's blood, there's fire, there's vapor of smoke. At the end of this age, before that great and glorious day, when Christ appears and sets his foot on the Mount of Olives, there will be these signs.

So verse 19, I think, is yet to come. It's part of this age, it's part of the same prophecy. We're in the age of the Spirit. It could happen today. And that's why it's presented as one smushed together thing, even though there's 2 ,000 years that span across this prophecy.

It's presented as one thing because it's all the church age. And we have no clue how long this will be.

We weren't told.

Could have happened that very day. And so Peter's quoting Joel. I will show wonders in the heavens above, signs on the earth below, blood and fire and vapor of smoke. The sun shall be turned to darkness, the moon to blood before the day of the Lord comes.

When will that come?

I wish I could tell you. But when I see Syria and Iran plotting together, and Israel surrounded by her enemies, a reborn nation of Israel in the promised land, Gog and Magog to the north. Then you go and you read Ezekiel 38 and 39, Isaiah 17.

You say, this might be sooner than later. This might be coming quickly. Listen, I don't know if it's gonna happen this year, within my lifetime or the next. We can't know that for certain, but the signs of the times seem to point to imminency, and even more so when you think that Peter expected it could have been his day.

We should look with expectancy to the heavens and say, Lord, are you coming soon? Lord, come soon. That's how Peter is preaching here. Some people say, you should avoid mentioning hell or anything scary in preaching the gospel.

The apostles did not have that concern, neither did Jesus. Jesus spoke of a place where the worm cannot die in an eternal flame. Peter was not afraid to warn of the dangers of hellfire, and here the dangers of the tribulation, a seven-year period of wrath upon the earth, the judgment of God beginning to be poured out on earth.

But notice that last verse, which spans the entirety of this church age, until Christ comes, verse 21, and it shall come to pass that everyone who calls upon the name of the Lord shall be saved. From that first day and that first sermon to as we sit here today, this offer is issued to us.

Believe in Jesus. Call upon his name. You will find him to be a perfect savior. Your sins can be forgiven. You can go down into the water, representing your death to your old man and come out of that water in newness of life.

Eternal life is offered to you on this day. If you will call upon the name of the Lord, you will be saved. This is the call to all mankind. It's issued freely without discrimination to all races, all people, young and old, men and women.

Turn to Christ.

Put your hope in him. Set your eyes upon him and believe in him. Turn away from your sin and turn to him. Call upon his name and you will be saved. Acts 2, 21. So this is the setup. And notice that Peter, when he is ready to preach the gospel, he takes the opportunity from the miracle that was happening.

But how did he do that?

Required two things. One, he knew Joel 2 by heart. How else could he preach it and quote it to them unless he enrolled a scroll in their very presence? How else could he know that what was happening on Pentecost was the fulfillment of Joel 2?

He was filled with scripture. But of course, the big point of Acts 2 is that he is filled with the spirit. So the word and the spirit filling Peter gives him the opportunity and the clarity and the boldness and the courage and the certainty to stand in front of thousands of people and proclaim Christ.

That's the first thing to notice today. We likewise need to be filled with the word of God. Knowing the word, studying it daily, letting it get into our hearts, meditating upon it so that we, like Peter, could quote it when we need it and understand how situations apply and live our lives by the word and to be filled with the spirit.

We all need that. Gospel preaching won't even happen unless we get to that point. Okay, so now we get to verse 22. And here's the question I want you to consider. One of the most important questions you'll ever be asked.

The Gospel Is the Person and Work of Christ

What is the gospel? There's a lot of different opinions about that, actually. You'd think that's a simple issue, but it's not. I think the answer will come to us from Peter. You wanna know what the gospel is?

Men of Israel hear these words. Jesus of Nazareth. The gospel is first and foremost the message of Jesus. It is the person, Jesus Christ, the Messiah sent from heaven.

It's declaring who he is.

It's taking the spotlight off of me and my life and my problems and turning the attention, shining that spotlight on the son of God. The person of Jesus is the beginning of the gospel. He's the alpha and the omega, the beginning and the end.

To understand the gospel, you need to speak of Jesus. Who is he? He's the son of God.

He's the son of man.

He's fully human and fully divine. He's the prophet who speaks for God, the final and ultimate prophet. He's the priest who stands between a holy God and a sinful man like me and as an intermediary, mediates the relationship between God the Father and a sinner like me.

And not only is he a priest who stands between, he is the very sacrifice that the priest offers because rather than bringing a bull or a goat to take away my sin, he brings his own body prepared for this purpose.

And he lays down on that cross and is sacrificed as the lamb of God. He's the priest but he's also the sacrifice and he's the king. The king who is coming to reign. And he was presented to Jerusalem, riding in on a donkey but rejected that day.

And yet he reigns. Already at the right hand of the Father, Psalm 110, we'll get to that. He's coming again to rule and reign on this earth for a thousand years before creating a new heaven and a new earth.

He is the king of kings, the Lord of lords. When he comes, his name, king of kings and Lord of lords, is written on his thigh. Jesus is the gospel. As John Piper says, God is the gospel. The gospel is this hope of heaven but what is heaven unless God is there?

He is the one we're going to. He is the destination. God is the gospel and Peter nails it, if I could say so. I'm learning from him, not the other way around. Man, this is a good sermon. Because the first words out of his mouth when he's ready to preach Christ is, Jesus of Nazareth.

He preaches Christ. He says he's a man attested by signs and wonders and various miracles that God did through him in your midst. Now we move on to verse 23. We've said the gospel is the person of Christ.

The gospel is also the work of Christ.

What do I mean by that?

Well, the historical facts of what he's come to do. He did these miracles but his greatest work was the cross. Verse 23, this Jesus delivered up according to the definite plan and foreknowledge of God, you crucified and killed by the hands of lawless men.

God raised him up, loosing the pangs of death because it was not possible for him to be held by it. The gospel is the person and the work of Christ. His work was to die on a cross, to be buried and on the third day to rise from the dead.

These are the historical facts that we must preach if we wanna have clarity, pure water to offer to somebody. We need to tell that the Savior died at Calvary's tree. We need to say they buried him but he rose from the dead because it was impossible for death to hold him.

He is a risen Savior. Our gospel is the death, burial and resurrection of Christ. But remember with many other words, Peter taught this truth. We also need to explain the meaning of these things. Notice here, Peter says it was by the definite plan and foreknowledge of God.

I kinda like feel that Peter is egging me on to bring my Calvinism to the table right now. That it was God's plan, his foreknowledge for Jesus to be crucified and killed by the hands of lawless men. I won't go down that road too long right now but to say the text says the plan of God, which is a decree, something that he had known in his foreknowledge, not because he learned it.

Go to 1 Peter chapter one. The son himself is by the foreknowledge of God. I think it's 1 Peter 1 .20 if I'm not mistaken. But it's in 1 Peter one. This foreknowledge is not a learned knowledge, it's the knowledge that God has in and of himself.

He knows these things and it was his plan, his foreknowledge that the son of God would be crucified by the hands of lawless men. It was decreed that Pontius Pilate and Herod and the Jews and the Gentiles would conspire and sinfully kill the innocent son of God.

That was God's plan. It included the sin of man. Now he always holds man responsible because they act according to their own hearts, their own desires. But the plan of God is in focus here and this is why this is so important.

No one took Jesus's life from him. He laid it down willingly in submission to the plan of the father. You see, when we talk about the death, burial and resurrection of Jesus, it's not enough just to be able to recite those facts.

We have to explain the meaning of these things. What is the meaning of this man attested by miracles who has the power to fight off these oppressors? He could have called the angels of heaven to rescue him in a second.

What's the meaning of this?

That instead he lays down and doesn't open his mouth to defend himself.

What does this mean?

The meaning of the cross is propitiation. That Jesus lays down his life willingly as a substitute to bear the wrath of God against sin. Now general revelation isn't gonna tell you this. You can't know this just by looking at the stars.

People need to hear that Jesus died for our sins. First Corinthians 15, three and four. When Paul summarizes the gospel, he says, I want to remind you of what's most important. He'll go on to say that Christ died for our sins according to the scriptures, that he was buried according to, and that he rose from the dead according to the scriptures.

Then he appeared. What does this phrase for our sins mean? Propitiation. It means that Jesus was lifted up on the cross to take the penalty of sinners like me. And the wrath of God that's owed to a man like me was not meted out into me such that I would go to hell.

Rather, it was placed on this substitute named Jesus of Nazareth. And he bore the wrath of God in his body on the tree, the righteous for the unrighteous to bring me to God. It takes many words to explain these things, but we need to bear into the scriptures to understand what's being taught here.

The reason for the death of Jesus was to justify a sinner like me, and you who believe in him. He died in our place, took the penalty that we deserve. That's the work of Christ. Now, we'll move quicker through the rest because at this point, Peter has preached the person and work of Christ.

That's the core content of the gospel. But he gives a basis for belief. The third major point is that the gospel appeals to the prophets and the resurrection. Look what Peter does here. By the way, guys, learn from Peter's methods.

When I share the gospel, I was on the plane flying home, and I sought to share the gospel. I was seated in the middle seat. I was actually tempted to buy the front row 1A when I was booking the flight because it was $45 extra, but I was like, man, I'd be on the front row.

And I said, ah, no, I can't do that because if I get the cheap one, I'm gonna be between two people, and I think I'm supposed to go there to share the gospel. Sure enough, there was a woman on one side and a man on the other, and so we just got to talking, sharing, talking.

Finally, I brought out my Bible to prepare my lesson, and she actually asked me if she could look on at the notes I was writing. I was working on this sermon, and I was like, sure, you can look on. So what I did is I just started writing the gospel as clearly as I could.

Jesus died for our sins, that kind of thing. And then the guy next to me, he didn't really ask, so after a while, I just asked him,.

Hey, you wanna read this?

Oh, sure, Peter's sermon. I was like, it's awesome. You gotta read the sermon, it's crazy. So he read it. We had these great conversations, but here's what I'm thinking when I'm sharing the gospel. One, preach Christ, his person, his work.

Two, I'm gonna appeal to the prophets and the resurrection. The prophets and the resurrection. That all of these things were foretold by prophets and came true in Christ, and that he rose from the dead and was seen by eyewitnesses who were willing to die for this testimony.

That's where Peter goes. So learn from the method, not just the content. So he's going to appeal to the prophets and to the resurrection. 25, for David says, well, why is he going to talk about David?

David's a prophet in this case. For David says, concerning him, I saw the Lord always before me, for he is at my right hand that I may not be shaken. Therefore, my heart was glad and my tongue rejoiced.

My flesh also will dwell in hope. For you will not abandon my soul to Hades or let your Holy One see corruption. You have made known to me the paths of life. Peter will take this passage from Psalm 16 and say, look, did David's body see corruption?

Sure did. He's rotting in a grave. But according to 2 Samuel 7, a son of David would always sit on the throne. Jesus is a direct descendant from David the king. Jesus is the true king.

David wasn't talking about himself.

He was talking about the Messiah. His body would not decay in the grave. He would rise from the dead. And that resurrection of Jesus was prophesied in Psalm 16.

David will go on.

I mean, Peter will go on and quote from David again in Psalm 110, verse 34. David did not ascend into heaven, but he himself says, the Lord said to my Lord, sit at my right hand. Psalm 110 is the most quoted Old Testament passage in the Bible.

The New Testament quotes that passage more than any other. It's the Lord, God, Yahweh, speaking to my Lord, Jesus, the Kurios, the Lord, saying sit at my right hand until I make your enemies a footstool for your feet.

The Father speaking to the Son, have a seat in your victory. After your finished work, having risen from the dead, ascended to the right hand of the Father, have a seat. The work is complete. And so this point number, what is it, five?

Verses 33 to 36 on your notes. The gospel assumes the authority to speak with certainty based on these prophets, based on the resurrection of Jesus from the dead. Verse 36, how does Peter finish? Let all the house of Israel therefore know for certain.

Now, the day in which we live, people hate that verse.

Why?

Well, we live in postmodern America, and what is postmodernity? It's the modernist experiment of the Enlightenment where everything was established by the scientific method, and knowledge could be attained, it was something outside of us, failing in the presence of two world wars.

And a disillusioned people who sought truth but only found it to be the bloodiest century in the history of the world, the 1900s, two world wars, Cold War, Korea, Vietnam. You have a generation of people who have thrown up their hands on truth itself and say, you know what, truth is just what you make it, there is no truth outside of us, and you can't be certain about anything.

Postmodernity is a war against certainty. You can have your own private beliefs, but don't claim that you know for sure. Don't claim that what you believe is true not only for you but for all people. That's bigoted, that's narrow-minded, that's intolerant.

Postmodernity, the mindset of our culture is that nobody can really know anything for sure, and yet Peter says in no uncertain terms, let all the house of Israel therefore know for certain that God has made him both Lord and Christ.

This Jesus, whom you crucified, he finishes where he started, Christ and him crucified. He proclaims with certainty, and now we get to the next point, this claim calls for a response. The gospel demands of all people, of all flesh, repentance from sin and faith in the Lord Jesus Christ.

Repentance and faith. So the people are saying, whoa, what should we do? Evidently the Spirit's working in them and they're believing what Peter is saying, so they say, what shall we do? Peter says, repent and be baptized, every one of you, in the name of Jesus Christ, for the forgiveness of your sins, and you will receive the gift of the Holy Spirit.

He calls for them to repent of their former way of thinking and their former way of living, to turn away from that, turn in another direction, and he speaks, I think, as a metonym here, where baptism represents that whole picture of conversion.

Remember, Peter is preaching a sermon to real people in time. He's not making a theological statement that baptism itself will be what saves you and give you the forgiveness of sins. By the way, if you want proof of that, Acts 10, verses 44 to 48, while Peter was still speaking, the Holy Spirit came upon them.