From the Heart by B.Demaere

So put away all falsehood and" tell your neighbor the truth" because we belong to each other.  And "don't sin by letting anger gain control over you". Don't let the sun go down  while you are still angry, for anger gives a mighty foothold to the Devil. I used to be very angry and now I have mellowed out quite a bit, just ask my wife and children.  It is also called not having a filter, you know? The kind that filters your words.  Keeping your mouth shut at the right time can keep you out of trouble and not say the stupid thing you really want to say at that time is also a good idea. Anger is very destructive and like a tornado it leaves a path behind it of unhappy customers, friends and family.  It also brings a lot of loneliness.  Who really wants to be around someone who is angry all the time. So that's what the words, "don't sin by letting anger gain control over you" mean, keep cool.  You can be angry but also think of your actions afte