Paul proclaimed he was in prison because he was Christ's prisoner. Why? Because he proclaimed the Gospel of the Lord Jesus Christ uncompromisingly without fear of retribution. He served the living Christ and succumbed neither to the wiles of Satan nor to the demands of the secular world.
He gives all the glory to God and in so doing proclaims: the grace of God; knowledge in the mystery of Christ, as it is now revealed unto his holy apostles and prophets by the Spirit; that the Gentiles should be fellow heirs, . . . and partakers of his promise in Christ by the gospel. He became Christ's minister by God's grace and His effective power working in him. God does this to enlighten and to strengthen each individual professing faith in Christ and endeavoring to walk with Jesus along life's pathway while enjoying blessings and gifts, as well enduring trials, tests, and temptations.
Paul was the ultimate pastor and teacher in expounding Christ's teachings. He was a God server, not a man server. May those who preach and teach follow in Paul's footsteps by proclaiming God's entire Word faithfully.