Like Jews and Muslims, Christians are monotheists. In other words, they believe in the existence of precisely one God. Unlike other monotheists, however, Christians also believe that, while there exists just one God, He is three persons—Father, Son, and Holy Spirit. The belief that the one and only God exists eternally as three persons is known as the doctrine of the Trinity. And this doctrine plays an important role in Christian faith. In fact, the doctrine of the incarnation—which says that Jesus as God became a man and that He is thus both fully divine and fully human—assumes it. This latter doctrine lies at the heart of Christian faith.

On its face, however, the doctrine of the Trinity might look like a contradiction. It might seem impossible that God be both one and three. Indeed, the apparent absurdity of this doctrine has led to at least two major errors, each of which elevates one of the doctrine’s claims at the other’s expense. On one hand, some stress the oneness of God at the expense of His threeness, claiming there is only one divine person. Those who describe God in this way usually say that the one divine person appears in different guises or masks, sometimes as Father, other times as Son, and still other times as Spirit. Since this view says the one divine person changes His mode of appearance, it is called modalism. On the other hand, some stress God’s threeness at the expense of His oneness, claiming each of the three divine persons is a distinct god. This view, which says that there are three gods, is called tritheism.

But modalism and tritheism are at odds with the Bible, which presents God as both one and three. There is just one God (Dt 6:4), yet this God is three persons—Father, Son, and Spirit (Mt 3:16-17; Mk 1:9-11; Lk 3:21-22). No doubt it is difficult (or perhaps even impossible) for us to understand how God is both one and three. But something’s being difficult (or even impossible) for humans to understand doesn’t make it a contradiction.

Those who think the doctrine of the Trinity is contradictory misunderstand either the nature of a contradiction or the doctrine itself. Perhaps they confuse contradiction with mere paradox, taking our inability to understand how the doctrine is true to entail that it is false. But our inability to understand how God is both one and three tells us far more about ourselves than it does about God. The Bible presents God as both one and three; that suffices for us to know that He is so, regardless of whether we understand the how of it.