Some people in the Corinthian church have been challenging Paul's authority. It appears that they have accused him of being "stern" in letters but not so challenging in person and some more aggressive members of the community have used this to stir dissent and division in the Church. Paul's response to this is to place himself, not in the position of power and control, but along side Christ who emptied himself and became a servant (see Philippians 2). Paul says it is pointless to pass judgment on him since there is only one judge (Jesus) and when judgment day comes everything will be revealed about everything.
He continues his argument by noting that the Apostolic life is the hardest of all. The Apostles have been put on display (see 8-11) and are "fools for Christ." I had a friend, Andy, who had a T-shirt that said "I'm a fool for Christ, whose fool are you." It is an unspoken but inevitable conclusion of life that everyone is a servant of someone or something or some "idea" or "ideal". Paul says in one of his other letters that we are the servant of whatever we submit or surrender to. We are wired in such a way that something has to have first priority in our lives. It might be self preservation, it might be a political ideal, or it might just be one of the primary idols of our culture: money, sex, power or self. Notice the litany in verse 11: "we are hungry and thirsty, we are poorly clothed and beaten and homeless, and we grow weary from the work of our own hands. . . " They apostolic life -- the life of preaching the gospel in new places to new people -- was a very difficult life, indeed.