Understanding the Trinity

In no other subject is error more dangerous, inquiry more difficult, or the discovery of truth more rewarding.

Augustine, De Trinitate

The doctrine of the Trinity poses a deep and difficult problem. On the one hand, it says that there are three distinct persons—Father, Son, and Holy Spirit—and that each of these persons "is God." On the other hand, it says that there is one and only one God. So it appears to involve a contradiction. It seems to say that there is exactly one divine being and also that there is more than one. How are we to make sense of this?

This is a difficult question, but one that Christians ought to take seriously. The difficulty is not just that the doctrine of the Trinity is mysterious. Rather, it is that the doctrine appears to be logically inconsistent—the sort of thing that could not possibly be true. And yet we must believe it if the rest of our faith is to make sense. For example, the Bible forbids us to worship any being other than God (see, for example, Exod. 20:3-5; Isa. 42:8). So Jesus is worthy of our worship only if he is God. But the Bible also makes it clear that the Father deserves our worship (see, for example, Matt. 5:9-13; Matt. 7:21; John 2:16) and that Jesus is not the Father (see, for example, Matt. 24:36; Luke 22:42; John 1:14, 18). So, if we are to go on worshipping both Jesus and the Father, we have to say that Jesus is God and that the Father is God. But, again, we cannot say that Jesus is the Father, nor can we say that they are two Gods (Deut. 6:4). The same is true in the case of the Holy Spirit (see, for example, John 14:26; Acts 5:3-4; Rom. 8:26-27).

Theologians and philosophers throughout the ages have devoted a great deal of effort to trying to understand the doctrine of the Trinity. Here we will summarize some of the fruits of their labor. We begin with a brief discussion of the doctrine in historical context, explaining more fully the nature of the problem it raises. We then turn to the most important strategies developed by Christians to resolve this problem.

The Problem of the Trinity in Historical Context

The doctrine of the Trinity says that God exists in three persons: Father, Son, and Holy Spirit. But that is not all it says. The central elements of the doctrine are neatly summarized in a passage of the Athanasian Creed, one of the most widely respected summaries of the Christian faith:

We worship one God in Trinity and Trinity in unity, neither confusing the Persons, nor dividing the substance. For there is one person for the Father, another for the Son, and yet another for the Holy Spirit. But the divinity of the Father, Son, and Holy Spirit is one. . . . Thus, the Father is God, the Son is God, and the Holy Spirit is God; and yet there are not three Gods, but there is one God.

This passage offers a paradigm statement of the orthodox understanding of the Trinity. As it makes clear, the doctrine requires not only that God exists in three persons but also that each of the following is true as well:

1. 1. There is exactly one God.

2. 2. The Father is God, the Son is God, and the Holy Spirit is God.

3. 3. The Father is not the Son, and the Holy Spirit is not the Father or the Son.

But these three claims are in obvious tension. The first insists that the doctrine must be interpreted in the context of monotheism, the view that there is one and only one God. But the second claim insists that each of the persons is divine, whereas the third tells us that there are three persons. Apparently, then, the doctrine says both that there is and there is not exactly one God.

It is important to emphasize that...