In Galatians 5:22-23, Paul is talking about practicing the things that are of the fruit of the spirit - "love, joy, peace, long-suffering, kindness, goodness, faithfulness, gentleness, self-control. Against such there is no law."
Self control is something that makes us realize that there is something ABOVE ourselves. In Peter's second letter, he says if we LACK self-control (among other things) - that we will be short-sighted, even to blindness. But if we practice these things (self-control, knowledge, Godliness, perseverance) - we will NEVER be unfruitful or barren in the knowledge of Jesus Christ.
Self-control shows respect to God and shows him that we long to please him.