"Of this church I was made a minister according to the stewardship from God bestowed on me for your benefit, that I might fully carry out the preaching of the Word of God, that is, the mystery which has been hidden from the past ages and generations; but has now been manifested to His saints, to whom God willed to make known what is the riches of the glory of this mystery among the Gentiles, which is Christ in you, the hope of glory," (Colossians 1:25--27).
* In his distinctive role as the apostle to the Gentiles, Paul's commission was to fully carry out the preaching of the Word of God-- particularly the truth concerning the church. The fact that regenerated Gentiles and Jews would both comprise the body of Christ had not been revealed in the Old Testament. And to each and every believer, God wills to make known the Lord Jesus Christ as his or her hope of glory.
* Two important qualities made the church a mystery -- as a spiritual organism comprised of both believing Jews and Gentiles, it was unknown to the Old Testament writers. And secondly, the permanence of Christ's presence in our lives had not been known in the Old Testament.
The irrevocable resident Holy Spirit confirms our future glorification with the Lord Jesus.