This was previously posted on Two Minute Theology.

In my previous post, I talked about why it’s important for Christians to know the Biblical basis for the doctrine of the Trinity, for the idea that God is one in essence and three in person. I discussed what it means that God is three in person. Now, let’s look into what it means that God is one in essence—a more complex topic.

Dr. Scott Horrell’s research suggests three Biblical truths that teach us that the Trinity is one in essence. Each truth alone isn’t enough to justify the phrase “one in essence,” but taken together they make a good case.

First, one essence means that the members of the Trinity share the same attributes. In many passages throughout the New Testament, the Father, Son, and Spirit are described as omnipotent, omniscient, omnipresent, holy, just, merciful, and all the other attributes of God. For many theologians, shared attributes is all that “oneness” is. But Dr. Horrell argues that this alone isn’t enough to distinguish Trinity from tritheism. For example, three separate gods could each hypothetically be perfectly omniscient.

Second, one essence means that the members of the Trinity “mutually indwell” one another. In John 14:7-11, Jesus says that anyone who has seen him has seen the Father, because he is in the Father and the Father is in him. Furthermore, he says that when he acts, it’s not just him, but also the Father acting. A similar mutual indwelling is suggested by the theme of Jesus’ relationship to the Spirit throughout John. So mutual indwelling can be summarized as the members of the Trinity each indwelling the others, so that when one acts, all are in some sense acting.

Third, one essence means that the very existence of the members of the Trinity is connected. The Bible suggests that the Son is eternally begotten by the Father (John 1:14, 18), and that the Spirit eternally proceeds from the Father (Gal 4:6)—and, in some views, from the Son as well (John 15:26). The nuances of what these terms mean have been explored by many theologians, but the upshot is that the members of the Trinity aren’t independent. The Son and Spirit’s existence is connected to the Father’s. It’s not that the Son and Spirit began existing at some moment in time; all of them existed from eternity past. But they did not exist in a disconnected way, but a connected way. We can’t fully understand this connection, because the Bible doesn’t go into it. We just have to affirm what the Bible does reveal: that there is a connection.

When added together, these three Biblical concepts seem to justify saying that God is “one in essence.” So the next time someone asks you to explain the Trinity, you can humbly say you don’t understand it fully, but you do know what the Bible teaches about it. You can say that God is three in the sense that the Father, Son, and Holy Spirit have real relationships with one another. And you can say that these three are one in the sense that they have a very close connection of essence: the same attributes, indwelling, and a connected existence.