22 But I tell you that anyone who is angry with a brother or sister, and says "You fool!" will be in danger of the fire of hell.
(meaning is coming from my Life Application Bible)
Meaning - Anger keeps us from developing a spirit pleasing to God. Have you ever been proud that you didn't strike out and say what was really on your mind? Self-control is good, but Christ wants us to practice thought-control as well. Jesus said that we will beheld accountable even for our attitudes.