There are so many rhetorical questions in chapter 9 of 1 Corinthians. It's almost like Paul wants to say, "Duh" to the church at Corith. What he is doing is pointing out the things he is giving up in his life or disciplining himself from so that he is a better witness for the gospel. He is making it clear that, although some of the things he gives up are not sinful to partake in, he abstains from such things to be set apart and free from guilt. Just like in chapter 8, where he explains he is free to eat or drink whatever he desires, he does not eat or drink certain things in certain situations so he does not cause someone else to stumble or judge him wrongly. Now in chapter 9 is goes further to explain the freedoms he gives up to better serve God.
Really, this is too short an explanation to do this passage justice, but to break down each statement would take me too long with my limited time to write. Basically, we need to look at the things in our lives that are not necessarily wrong to be involved in but that might cause others to stumble or question our faith. We need to be able to use our freedoms to further the kingdom of God and allow us to more easily share the gospel. Just as Paul says in 9:22 "...I have become all things to all people, that by all means I might save some," our freedoms allow us to present to gospel to all types of people. But we must, "discipline (our) body and keep it under control, lest after preaching to others (we) should be disqualified."