Paul saves some of his harshest words for the Corinthians in these chapters. There are two issues that are at stake: 1) the community that he founded was questioning whether Paul was actually an apostle, appointed by God, to be doing the type of work that he was doing. He certainly was not one of the 12 original disciples, so from where was he getting his authority. This leads him to "boast" about the work that he has done, including, look at chapter 11:23ff where he lists all of the times that his life was in danger because of the work for the Gospel. He admits that while his letters are powerful, his words might be a little less so.
The second issue was that of an offering that was supposed to be taken up that all of the other churches had taken up but the Corinthian church had not been required to do it as of yet. But Paul states that he is on his way to collect it, or he would send Titus to collect it for him. These two issues lead him to warn the community that as he is on his way to see them he tells them to examine themselves because when he comes he will drive out those who are involved in immoral deeds that is taking the community away from being the virgin bride that Christ wants his church to be.
I love 13:12 which states - "Greet one another with a holy kiss."