Rom. 15:18 I dare not boast of anything else. I have brought the Gentiles to God by my message and by the way I lived before them.
The Apostle Paul was saved to be a witness to the Gentiles of God's saving grace through Christ Jesus. It was what God commanded him to do. It was what he did with a passion. He was not very well-liked by his fellow Jews because of it. He was often beaten, thrown into prison, run out of town, and falsely accused before the Roman council because of it. Life was very difficult for Paul, but he could not be stopped.
Paul was a humble man and did not boast of his accomplishments. He could have taken pride in his birth pedigree, but he didn't. He could have boasted of his Roman citizenship, but he didn't. He could have boasted of all of his successes in the churches he helped establish and preached in, but he didn't.
The only thing that Paul pointed to was the fact that that he did what God told him to do. He brought many Gentiles to God through his preaching, teaching and living. His message was very clear and consistent wherever he went and he backed up his message with the way he lived.
The only real witness that we have that matters to the world is whether or not our living supports what we proclaim. It's not too hard to notice a hypocrite and the world jumps on them like fleas on a dog. The world may not agree with us when we live what we preach, but they do have to respect the fact that we live it. Let us always strive to show by our example of living that the Gospel message is for real and that it indeed does change lives.