When Paul referred to Jesus (Yeshua‘) as the Mystery of God, he did not have a modern concept of a mystery in mind. Biblical mysteries were things that only remained hidden for a season. In Christ, many of the secret things of God were revealed. Those that remain will one day be made plain to everyone. Paul mentions several revealed mysteries but the central one is Christ.
The Mystery of God in Greek:
To mystērion tou Theou
Strong’s Concordance numbers: 3466, 2316
Bible reference: Col. 2:2
In His letter to the Colossians, Paul said:
My goal is that they may be encouraged in heart and united in love, so that they may have the full riches of complete understanding, in order that they may know the mystery of God, namely, Christ. (Colossians 2:2 NIV)
The Message Bible calls Jesus “God’s great mystery.”