1. We who preach Christ, the mystery of God (1 Co 4:1)
    Col 1:26-27, Col 2:2, Rom 16:25-27

The mystery of God is Christ. Christ appeared. That is Jesus. (Col 1:26-27)

Col 1:26 Even the mystery which hath been hid from ages and from generations, but now is made manifest to his saints:
27 To whom God would make known what is the riches of the glory of this mystery among the Gentiles; which is Christ in you, the hope of glory:

We must make people aware of Christ, the mystery of God. We also need to make people realize that Jesus is the Christ. (Col 2:2)

Col 2:2 That their hearts might be comforted, being knit together in love, and unto all riches of the full assurance of understanding, to the acknowledgement of the mystery of God, and of the Father, and of Christ;

The gospel, which was hidden since the world began, and now revealed, is that Jesus is the Christ. (Rom 16:25-27)

Rom 16:25 Now to him that is of power to stablish you according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began,
26 But now is made manifest, and by the scriptures of the prophets, according to the commandment of the everlasting God, made known to all nations for the obedience of faith:
27 To God only wise, be glory through Jesus Christ for ever. Amen.