In this chapter, Paul seems to be vindicating his apostleship, but he doesn't want this to be with carnal, but spiritual weaponry. There were those in Corinth who questioned his apostleship which we read about in Acts 9, given by Christ himself. For myself, I am thankful for the letters of Paul included in the New Testament. Many of them were corrective and all of them instructive. It seems that they were the means of maintaining the doctrine of the Gentile part of the church, more than Peter and John, but they were important too.
Paul ends this section with the purpose of preaching the gospel to regions beyond. He through us and his teaching are reaching far beyond Paul's imagination. I am thankful to be preaching where I am with the freedom I have. Of course if I glory at all, I must glory in the Lord (vs. 17). It is not I but God who commends me if I am to be commended at all (vs 18).