12:19 The first part of this verse may have been a statement or a question. The meaning is the same in either case. Paul said what he did, especially in 10:1-12:18, primarily to build up the Corinthian believers in their faith. His self-defense was only a means to that end. It was for that worthy goal that he was willing to speak "foolishly."He recognized that he as a man in Christ was ultimately responsible to God, not to his critics (cf. 2:17; 5:11).
12:20 Paul feared that he might see qualities in his readers that he did not want to see if they refused to respond to his instructions in this letter. Furthermore he feared that they might see the disciplinarian in him. He also feared that he might sorrow if he saw continuing carnal conduct in them (cf. 1 Cor. 1:11-12, 31; 3:3; 4:6; 5:2, 11; 8:1; 11:18; 14:33, 40).
"It is an understatement to say that Paul was afraid of what he might find at Corinth upon his third visit. This list of sins reflects a church that was in turmoil. Little wonder that he was coming to correct the situation."284
12:21 Moreover he feared that he might suffer humiliation over their failure to repent of the attitude that had embarrassed him on his former painful visit. This situation would cause Paul to mourn over those in the church who had not repented of their former sins. The sins mentioned seem to have been unrelated to Paul's critics, though the critics may have practiced them as well. Paul's concern here seems to have been mainly the ungodly conduct that had marked the Christians in Corinth since the founding of their church.