The introductory phrase for I am not ashamed of the gospel adds a final mark of spiritual service to those presented in verses 8--15, the mark of unashamed boldness.
Paul was imprisoned in Philippi, chased out of Thessalonica, smuggled out of Damascus and Berea, laughed at in Athens, considered a fool in Corinth, and declared a blasphemer and lawbreaker in Jerusalem. He was stoned and left for dead at Lystra. Some pagans of Paul's day branded Christianity as atheism because it believed in only one God and as being cannibalistic because of a misunderstanding of the Lord's Supper.
But the Jewish religious leaders of Jerusalem did not intimidate Paul, nor did the learned and influential pagans at Ephesus, Athens, and Corinth. The apostle was eager now to preach and teach the gospel in Rome, the capital of the pagan empire that ruled virtually all the known world. He was never deterred by opposition, never disheartened by criticism, and never ashamed, for any reason, of the gospel of Jesus Christ. Although that gospel was then, and still is today, a stumbling block to Jews and foolishness to Gentiles, it is the only way God has provided for the salvation of men, and Paul was both overjoyed and emboldened by the privilege of proclaiming its truth and power wherever he went...