So let's just begin by discussing very quickly, when we talk about the doctrine of the Trinity, what is the basic doctrine? The basic doctrine is that we believe that God is one, Christians are monotheists, meaning we believe in one God, we don't believe in tritheism, which is the doctrine that there are three gods, we don't believe God breaks up into three parts, and we don't believe in modalism, which is that God is simply showing himself in three different modes, and we'll talk about that in a minute, but rather we believe that God is one in his essence, or one in his being, and so when we talk about God as one, we are talking about the being of God, God is one in his being, or one in his essence, and another word that we use sometimes is the word substance, and when I'm teaching on the Trinity, I say, that which God is in his substance is one, and you say, but God is spirit, so therefore God doesn't have substance, he doesn't have water, or fire, or some other substance that can be measured or weighed, and that's true, but when we talk about God in his nature, we talk about God in his being, we say God is one, and yet we also talk about God being three in a different category, and this is where the Trinity is very important because what is most important about the doctrine of the Trinity is that we understand category distinctions, because God is one in his essence, or his being, or his substance, but God is three in his person, or what we might call his subsistence, this is the way that some of the confessions refer to the persons, rather than saying person, they will use the phrase subsistence or peculiar relative properties is sometimes the way that it's described confessionally, and so when it's saying that, it's saying that there are three persons that share the one essence of God, there are three persons who are able to relate to one another, they are able to interact with one another, in fact we would say they're able to love one another, and that's an important part of the doctrine of the Trinity, is understanding that there is a love relationship within the Trinity, the Father loves the Son, the Son and the Father love the Spirit, the Spirit loves the Father and the Son, and that relational aspect of the Trinity is maintained in the doctrine of the Trinity which says God is one in his essence, but he's three in his person and he has always been three in person, it's not as if God became Trinity when he created the world or he became Trinity when he sent Jesus to be born of a virgin, or when Jesus was born of a virgin, that is not what we're saying, we're not saying that God became a Trinity, we're saying God has always been Trinitarian, and so in eternity past, which is kind of a miscommunication of terms, because when we talk about eternity we talk about past and future, but in a sense eternity is outside of time, so eternity past is kind of an odd way of saying it, but what we mean is before God created time, before God created the world and the universe that we now live in, he existed outside of time, and he has always existed, there was never a time when God was not, and there was never a time when God was not Trinitarian so God has always been one in essence, God has always been three in person, and there is a distinction between being in person, or essence in person or substance in subsistence, and I do use this analogy a lot, so if you've heard me use it before I just remind you that repetition is the key to learning, and the key to learning is repetition so it's okay if you've heard this before, and this again did not come from me, but a lot of my early instruction on the doctrine of the Trinity, I was helped greatly by Dr.