At first glance, it seems that the two statements are contradictory. There is only one God, yet there is God the Father and God the Son and one is not the other. To explain exactly how this works, though, has tongue-tied many people throughout the centuries. Add to this another complication as Christians also believe the Holy Spirit is God, and yet He is distinct from the Father and from the Son. How can such a seemingly illogical position be true? The answer lies in the concept of the Trinity,
The Trinity – What is it?To describe the Christian belief of the Trinity is actually quite simple, but it takes a bit of careful thinking to make sure the concept is properly understood. To say God is a Trinity is to say that God is one being comprised of three persons. The term "Trinity" was first used for the three persons comprising God by the early Church father Tertullian around AD 200.1 Tertullian saw a distinction between what it means to be a person and what it means to be a being. Our difficulty today is primarily because most people think the terms are synonymous. We see a person and we say that the person is a human being. One person = one being.
However, it isn't always the case that the attributes of a being are the same as the attributes of a person. To prove my case, let's proceed downward rather than upward. When Tertullian talks about a being, he means that there is one substance that makes up the entity of God. When we look at our own bodies, we see that every part that properly belongs to our body should be considered human. Every cell is a human cell. We are made up of human "stuff" if you will. Similarly, every part that makes up a plant is "plant stuff." A plant is also a being; it is a living thing that exists. But no one would claim that a plant is a person. That would be foolish!
So, we have two cases here. We recognize a plant as a being, but it has no personhood within it. It has a personhood count of zero, if you will. We also recognize a human as a being that has a personhood count of one. This means that personhood is different from being, as a being can exist without personhood. It then follows that it isn't contradictory to say that God is a being with a personhood count of three. It may be the case that we see no parallel here on earth, it may be the case that there is no other being in all of reality that can claim multiple personhood. However, it is clear that the claim of one being in three persons is not a contradiction, any more than claiming a plant is a being with no personhood should be considered such.
The Trinity – Its NecessityThe Bible clearly recognizes God the Father as God. That claim is usually not disputed. However, as I mentioned last time, it also recognizes Jesus as God and it identifies the Holy Spirit as God, too (Matt. 28:19, Acts 5:3,5, Isa 63:10, 1 Cor. 2:10-11). These three persons are each recognized as fully God and yet God is one. If one denies the triune nature of God, then one is forced into denying some portion of scripture.
Beyond the reconciliation of Scripture, the doctrine of the Trinity holds additional advantages. I've argued this before, but it is through the relationship within the Trinity that God can be considered completely without need. Only a being like the Trinity can be all-loving, and only within a trinity can God express His own humility.
Of course, no one can say exactly how all the aspects of the three-in-one work. That shouldn't be a surprise, though. Scientists today have really good data on quantum models of matter, but you don't have to be able to explain all aspect of quantum mechanics to believe it's true. When talking about God, one is referring to a being that transcends humanity; therefore one should expect that there would be aspects to His nature beyond our comprehension. But that doesn't mean that we cannot apprehend the basic understanding of the Trinity. God is three persons who comprise one being and each is fully God.