What does Paul reveal about the nature of God as part of the mystery?
Paul reveals that God is Father, Son, and Holy Spirit—a triune God. This Trinity is part of the mystery, a revelation the Old Testament is vague about, though it contains evidences. All treasures of wisdom and knowledge are hidden in God and Christ.
Les explains that the mystery includes God the Father and Christ, in whom are hid all the treasures of wisdom and knowledge. The revelation the Old Testament is vague about is the Trinity. Though the Old Testament has evidences of the triune God, Hebrews and rabbis even today call Christians pagan, saying we worship three gods, because they do not recognize the Trinity. Paul brings out that part of the mystery is that God is the Father, the Son, and the Holy Spirit. Later in 1 Corinthians 15 Paul again speaks of a mystery, first about Gentiles becoming one with God, then about God and the revelation of who He really is as the triune God.