I want to start by laying out five biblical propositions that form the basis of everything we can and must say about the Trinity. They are:
- 1. There is one God
2. There is a Person called the Father who is God
3. There is a Person called the Son who is God
4. There is a Person who called the Holy Spirit who is God
5. These three Persons are distinct (that is, the Father is not identical to the Son or Spirit, nor is the Son identical to the Spirit)
I would start by noting that to take (1) seriously is to affirm that there is only one divine nature. It should be clear that if there were two or more divine natures, then there would be no way to say that both are God. For if there were two, then the two natures would have to be different in some way, and then that would mean that one is God and the other is not. Further, if there were two or more divine natures, then (2)-(4) would not be true, or they would at least be meaningless, because the word “God” would have to mean different things in each sentence.
Second, notice that if there is only one divine nature, then it is common to all three Persons. Now, there are two ways we can take that sentence. First, we can say that the nature is common to the Persons in the sense that my wife and I have a common human nature. In this way of thinking, the divine nature is a really existent reality apart from any of the Persons themselves, and that the Persons have and in some sense exhibit that nature. To stick with my example, “humanity” is a really existent nature. My wife and I each have and exhibit it. But I would submit to you that this cannot be what we mean when we say that divine nature is common to all three Persons. Because if that were the case, we would have three beings exhibiting a common nature, which would be tri-theism. That would be in contradiction with (1).
Third, I would note that if there is only one nature, then there can be no distinction between the Persons at the level of nature. One common misconception to illustrate this: people often tend to think that the Father, Son, and Spirit all have their own wills, and that these three wills are “one” in the sense of being in agreement. But two distinct wills means two distinct natures. In fact, there is exactly one will in God, and that one will is common to all three Persons. In short, if we propose any distinction between the Persons that would require multiple natures, then that distinction is false and must be rejected.
So how can we distinguish between the Persons? Since we cannot distinguish at the level of nature, and since we cannot distinguish at the level of bodies (which is the way we distinguish between material entities of the same nature—you can distinguish between my wife and I even though we have a common nature because, while our nature is identical, we are different instances (different bodies) of that same nature, and so we are more than one; we are two), there is only one option left: we distinguish between the Persons via their relations.
Let me explain. In (2)-(4) above, we identified three Persons: Father, Son, and Spirit. The Father is related to the Son, and the terms “Father” and “Son” implicitly tell us something about their relationship. The Father’s relation is what we call “paternity.” The Son’s relation is what we call “filiation.” Where there is paternity, there is necessarily filiation, and where there is filiation, there is necessarily paternity. Paternity is not filiation, and filiation is not paternity, so this distinction in real. Yet the Scriptures tell us of a third relation. His name is “the Holy Spirit,” so we call that relation “spiration.” Now, this is important: the Son is begotten of and proceeds from the Father. So, too, does the Holy Spirit. But if the Son proceeds from the Father and the Spirit proceeds from the Father, then how do we distinguish between them? Remember, the only way we can distinguish between the Persons is via relations! This is why the Western Church claims that the Spirit proceeds from both the Father and the Son. So we see the three Persons are distinct by their relations only. The Father is the Father because He begets the Son; the Son is the Son because He is begotten by the Father; the Spirit is the Spirit because He proceeds from both the Father and Son.
So, fine, the Persons are distinguished only by their relations to each other. But relations necessarily require two or more entities, and if there is only one divine nature, what is related to what? It isn’t enough just to say “the Father is related to the Son,” because, remember, the Persons are nothing more than the relations. Such an answer, while perhaps true as far as it goes, just begs the question. So the classical answer here is that the relations are between the divine processions.
Ok, so what are the divine processions? There are two: the procession of the intellect and the procession of the will. For reasons I won’t bore you with here, there can be no more and no less than these two processions. So let’s take them in that order. An intelligent, rational entity necessarily has an intellect. It knows things. In God’s case, what He primarily knows is Himself—His own infinite nature. He knows it completely, fully, absolutely. The self-knowledge of God is called a “procession,” insofar as God’s knowledge of Himself “proceeds” from His very nature. A second procession is the will, for all volitional entities will things. Now, what God primarily wills is Himself (for reasons, again, I won’t bore you with; it has to do with the will necessarily being related to the good and God being the very nature of Good-in-itself). Thus, like God’s self-knowledge is a procession, God’s self-willing is a procession.
I want to pause here, because it might be tempting to identify the nature as the Father, the procession of the intellect as the Son, and the procession of the will as the Spirit. But that would fail, because that would mean that the Father had no intellect or will in Himself (but only relative to the other two Persons), and thus He would be incomplete. That is, He would be imperfect, and therefore not God. Just so with the Son, who would lack a nature and will, and the Spirit, who would lack a nature and intellect, and thus neither would be God. The point is that it is the relations that are related to one another. And that is where we see that one relation is called paternity, one relation is called filiation, and one relation is called spiration.
So there are a lot of other technical questions we could get into, but I don’t want to press things too far. I’m already close to 1500 words, so let me stop here. I just want to offer something that I hope is helpful in giving people a start on what “the Trinity” entails. Each of the three Persons are identical the one divine essence, but the three relations are necessarily distinct, not by nature or essence, but by their relation one to another, as paternity (Father), filiation (Son), and spiration/procession (Spirit). As such, all three Persons share a common nature even as they are distinct one from another. All three are absolutely identical at the level of nature and there is nothing to distinguish them save these relations. In other words, one God subsisting in three Persons, all of whom are distinct from one another even as they are identical with the divine essence.