Paul was not ashamed to preach the gospel and make it central to his missionary activity. His confidence was due to his understanding that the gospel is God's powerful way of saving sinners. He realized that the good news of the person and work of Christ delivers guilty sinners from condemnation, providing them with a standing of perfect righteousness before God. He also realized that the gospel works transformation in the lives of formerly enslaved sinners making their practical lives look more and more like their perfect standing.