What did Paul mean when he described himself as a servant of Jesus Christ?
Paul meant he was a bond slave of Jesus Christ, not merely a servant in the ordinary sense. The Greek word is stronger than the English term servant. He was called to be an apostle and separated unto the Gospel of God, as the apostle of the Gentiles.
Les explains that the word servant in the Greek is much stronger than our word servant; it really means a bond slave. So Paul opens the epistle by saying, in effect, Paul, a bond slave of Jesus Christ, called to be an apostle, separated unto the Gospel of God. In the surrounding context, Paul is the one God saved out of Judaism and commissioned to be the apostle of the Gentiles, as stated in Romans 11:13. Les notes that although others such as Barnabas and Silas were reckoned as apostles, Paul is uniquely the apostle of the Gentiles, and his letters alone are written to the Church, addressing believers of grace by faith alone.