Cain was angry with Able in Genesis 4:7, and God told Cain to master it!
How can we master anger?
When I was younger I had an anger problem, everyone and everything made me angry until I learned to recognize anger. Anger is a feeling. When it starts to grow you can literally feel your emotions start to boil. Anger can be mastered as soon as it starts by purposefully stopping and asking yourself, why is this angering me?
Taking the time to think about the reason why and even of the consequences of an outburst can help you put the offense into the correct perspective, calming your emotions.
Remember, Jesus said it is O.K. to be angry, but it is not O.K. to sin in that anger. Most of the time our outburst of anger is sin and we know this because we later regret what was said and even regret the outburst.
When we master our anger we are fighting against the works of the flesh and displaying the fruit of the spirit, self control.