It is the account of Paul's prayer to God to remove the affliction which had hounded him for many years. It is significant to notice that both the thorn and the 3rd Heaven appear in the same chapter. The issues of suffering and glory are not mutually exclusive. On the contrary they are twin sisters. The experience of suffering is the one of the primary ways by which Christians learn how to walk with God.
Human beings learn by experience.
No experience in the Christian's life is wasted because God will use each one to bring us to maturity. As a matter of fact, we learn more truth in our thorn experiences than we do from our 3rd Heaven experiences. Paul had prayed three different times for God to remove this horrible affliction from him. Because of this, Paul's attitude toward the thorn changed. He learned to appreciate the thorns of his life and let God's power work through them.