Paul seems to be defending himself in this section of his letter. Apparently, there were some drawing divisions between him and the apostles who had actually walked with Jesus, possibly even saying that he was somehow lesser. His response is direct: I am an apostle because I have produced the fruit of an apostle, and you are that fruit. Perhaps because of this strong stance, he also backs off a bit, reminding the Corinthians of the importance of building one another up by joining the struggles of others, as he did often.