Not only was Paul not ashamed, but he was not cast down, nor does one word of resentful anger escape his lips because of the unrighteousness of the world and the desertions, ingratitude and even opposition on the part of many Christians.
Paul is lifted above all depression, all resentment and all rancor, inasmuch as he is persuaded that Christ is able to keep that which he has committed unto Him against that day.
When Christ was reviled, He reviled not again, when He suffered, He threatened not, but committed Himself to Him that judges righteously. In the spirit of his Master, Paul, in the presence of suffering, desertion and insults, commits everything into the hands of Christ. His honor, his reputation, his character, his vindication and his happiness all are committed to Christ, knowing that, though the saints may desert and even oppose him, Christ will never fail him. He is persuaded that Christ is able to care for his interests, vindicate his honor and right every wrong in that day.
H. Smith (from Gems From My Reading)