In this section, Paul is thanking them for their care of him. He is also acknowledging there has been some uncomfortable exchanges. He asks them "Have I become your enemy by telling you the truth?"
There are few tasks as difficult for a pastor than to tell the truth. Our culture teaches us to "mind our own business," and to "let folks make their own decisions". Those well learned lessons don't sit well with telling the truth about some behaviors or words or beliefs.
Too often we ignore those things in the lives of others which impede their ability to show forth Christ. Too often we remain silent even when we become aware of that which runs contrary to the word and will of God. It is as if we are more fearful of becoming another's enemy than leaving them in their sin.
The followers of Jesus are to admonish one another. This is an important task. It is how we assist one another in their witness. Rather than become angry, we are to be thankful that another cared enough to point out to us what we had failed to see.