Ephesians 4:26 - Coke's Commentary on the Holy Bible

Be ye angry, and sin not:— It is evident that this is not a command to be angry, but a concession only, with a caution to beware of sinning in it. Comp. Isaiah 8:9-10. Nahum 3:14-15. Some would read this interrogatively,—Are ye angry, yet sin not? The next is a Hebrew expression,—used to intimate that a thing necessary to be done, should not be prolonged or delayed;—and an allusion to Deuteronomy 21:23 to this effect: "If thepunishments inflicted by the law were not to be extended to the going down of the sun, much less should private resentments be extended longer." This was agreeable to the practice of the Pythagoreans, who used always, if the members of their sect had any difference with each other, to give tokens of reconciliation before the sun went down.