Many Christians throughout the centuries have offered varying interpretations of the verse “be angry and sin not.” In this sermon on anger from Ephesians 4:20–27 titled “Sinful and Righteous Anger,” Dr. Martyn Lloyd-Jones discusses how Christians should apply this command to their lives. He contends that Paul is not saying that one can be angry as long as they don’t sin— it is not a permissive statement. Rather, Paul is saying that there are certain things where anger is acceptable as long as the Christian does not sin in their anger and give a foothold to Satan. Anger, he says, is a natural capacity given by God against the things that dishonor Him and what He declares to be good. As Dr. Lloyd-Jones points out, even Jesus is recorded in the gospels as becoming very angry about unrighteousness in the temple. The key to understanding this verse is that anger must be directed towards the things that God hates but ultimately, Paul is calling Christians to avoid sin and to be angry towards it. Dr. Lloyd-Jones declares that anger against sin is being increasingly explained away by the world, but Christians must be faithful to hold it for what it is— an affront against God.

http://www.mljtrust.org/sermons/sinful-and-righteous-anger/