"Be angry, yet do not sin": This verse quotes Psalm 4:4. The literal form of the quotation does not justify anger. Anger gives the devil an way to influence us (see James 1:20). God's people should be gentle and gracious, not harsh or angry (see Ephesians 4:31–32).
Do not let the sun set upon your anger: This means we should resolve our anger quickly. We should not allow our anger continue or grow stronger.