What did Les think Paul's thorn in the flesh was?
Paul's thorn in the flesh was understood to be a repulsive, painful disease that Paul carried throughout his life, not a specific named condition. God did not heal it, and His grace sustained Paul through it.
Les explains that Paul besought the Lord three times that the thorn might depart, but God did not heal him of whatever it was. Les says he has an idea but probably no room to express it, yet he has a pretty good idea what Paul's malady was: a repulsive, painful disease that Paul took with him all the days of his life. God told Paul, "My grace is sufficient for thee," and that grace carried Paul through his ministry, shipwrecks, beatings, hunger, cold, and nakedness. Les applies this to believers, who must rest on the fact that God will take them through whatever He sees fit to take them through, and His strength is made perfect in weakness.