The Christian faith doesn’t talk of three gods, each with the potential of wandering off in his or her own direction, perhaps even launching war against the other gods. For example, the Ten Commandments begin, “I am the Yahweh your God, who rescued you from the land of Egypt, the place of your slavery. You must not have any other god but me” (Exod 20:2–3, also Deut 5:6–7)
So Israel’s confession was, “Yahweh is our God, Yahweh alone” (Deut 6:4). So Isaiah reminded Israel of God’s demands on this count: “I am the Yahweh; that is my name! I will not give my glory to anyone else, nor share my praise with carved idols” (Isa 42:8). And this is the New Testament’s confession too (Jas 2:19).
Orthodox Christianity holds that all three persons of the Godhead are in total unity with one another and fully involved with any particular work of the Godhead. Systematic and historical theologians use a variety of technical terms to expression this integrated unity, such as perichoresis and coherence, or Latin technical terms like circumincessio and circumcessio.
I won’t argue for particular technical terms for the mutual indwelling of the persons or try to define it metaphysically. Rather than waxing eloquent along philosophical lines, the way we’ll talk about the Trinity is to speak of the Godhead as “one being in three persons” and then show how the Bible requires that twofold understanding.
One in Nature
The Scriptures show us that God is One, which is in itself a fairly philosophical sounding assertion.
Jesus and the Father
But when we move to God’s self-revelation in Jesus Christ, we hear Jesus speaking of himself in terms that reflect one nature in the Godhead. When people ask if he’s the Messiah, he points to the works that he does in the authority of the Father (John 10:24–25). But he goes further: “The Father and I are one…. understand that the Father is in me, and I am in the Father” (John 10:30, 38).
So when Philip asked, “Lord, show us the Father, and we will be satisfied.” Jesus replied, “Have I been with you all this time, Philip, and yet you still don’t know who I am? Anyone who has seen me has seen the Father! So why are you asking me to show him to you? Don’t you believe that I am in the Father and the Father is in me? The words I speak are not my own, but my Father who lives in me does his work through me. Just believe that I am in the Father and the Father is in me. Or at least believe because of the work you have seen me do” (John 14:8–11).
Jesus and the Spirit
And Jesus implied that he shared the same union with the Spirit that he had with the Father. He told his disciples, “I will ask the Father, and he will give you another Advocate, who will never leave you. He is the Holy Spirit, who leads into all truth.” So there’s Jesus talking about the Spirit in the third person. But he closed out that promise in the first person: “I will come” rather than “he will come.” Jesus said, “I will not abandon you as orphans—I will come to you” (John 14:16–18).