and do not give the devil a foothold.If you do not deal with your sinful anger in a Biblical way, then you can rest assured that the devil will get a foothold into your heart and mind.
The devil here is the word that means, false accuser or slanderer. Sinful anger can play just such a role in your life, it can deceive you and trick you. The longer you allow it in your life, the more it can twist your thinking.
[Personal Note:] As I am writing this, I am being reminded of all sorts of times in my life that I held onto anger, and in my 20/20 hindsight, I can see how the devil did receive that foothold. I don't know why I never saw this connection before, this connection between anger and self-deception. When you get angry, and don't deal with it in a proper way, you become more and more focused on whatever it is that has made you angry. In the end, you have completely forgotten the greatest command of God, to Love Him and to Love Others.