Adam Clarke on Ephesians 4:26

Be ye angry, and sin not - Οργιζεσθε, here, is the same as ει μεν οργιζεσθε, If Ye be angry, do not sin. We can never suppose that the apostle delivers this as a precept, if we take the words as they stand in our version. Perhaps the sense is, Take heed that ye be not angry, lest ye sin; for it would be very difficult, even for an apostle himself, to be angry and not sin. If we consider anger as implying displeasure simply, then there are a multitude of cases in which a man may be innocently, yea, laudably angry; for he should be displeased with every thing which is not for the glory of God, and the good of mankind. But, in any other sense, I do not see how the words can be safely taken.

Let not the sun go down upon your wrath - That is: If you do get angry with any one, see that the fire be cast with the utmost speed out of your bosom. Do not go to sleep with any unkind or unbrotherly feeling; anger, continued in, may produce malice and revenge. No temper of this kind can consist with peace of conscience, and the approbation of God's Spirit in the soul.