Why was Paul not ashamed despite all his suffering?
Paul was not ashamed because he knew whom he had believed. Though he suffered as a preacher, apostle, and teacher of the Gentiles, with opposition from Judaism and satanic power, he never doubted the God he served. His confidence rested in God's purpose and grace given in Christ Jesus before the world began.
Les teaches that Paul suffered because his appointment as a preacher, apostle, and teacher to the Gentiles stirred opposition. His chief opposition included Jews, both believing Jews and those still steeped in Judaism, but it was also a satanic power from every direction, because Satan did not want the gospel going to the Gentile world. In spite of all his difficulties, sickness, sorrow, and suffering, Paul never once doubted the God whom he served. He was not ashamed, for he knew whom he had believed, and his calling rested not on works but on God's own purpose and grace given in Christ Jesus before the world began and now made manifest through the gospel.
For the which cause I also suffer these things: nevertheless I am not ashamed: for I know whom I have believed, and am persuaded that he is able to keep that which I have committed unto him against that day.