SPROUL: I don’t think the average New Testament Christian is able to gain a complete understanding of the Trinity. I suppose that what you mean is, “Can you find the Trinity in the Old Testament?”
I think you have to be careful about how you understand the Old Testament. The Old Testament, in a progressive fashion, points us to a fuller revelation that comes forth in the New Testament. I don’t think it’s foreign to the Old Testament. It’s the old statement that the New is in the Old concealed, and the Old is in the New revealed.
THOMAS: This is a good question. It forces us to be careful how we negotiate seeing the Trinity in the Old Testament because there is a stubborn fact that no Old Testament Jew—whether Isaiah or Ezekiel or Amos—ever propounded a doctrine of the Trinity. So, when we say that God’s name is plural, Elohim, or when we conjecture from the appearances of God in the Old Testament as anticipations of plurality within the Godhead, none of this seems to be apparent to any Old Testament writer.
If there’s one thing that’s true of Old Testament Jews, it was their insistence that God is one. Therefore you have the repetition of the Shema, that passage in Deuteronomy 6:4: “Behold, the Lord your God, He is one.” So, although I think the Old Testament is conducive to an interpretation of plurality, it wasn’t apparent to the Jew in the Old Testament that it was.