Albert Barnes Commentary Proverbs 20:22

"Say not thou, I will recompense evil: Wait for Jehovah, and he will save thee." — Proverbs 20:22 (ASV)

God's awarding to everyone according to his works, is the true check to the spirit of vindictiveness (compare Romans 12:17, Romans 12:19). Note that man is not told to wait on the Lord in expectation of seeing vengeance on his enemies, but He shall save thee. The difference of the two hopes, in their effect upon the man’s character, is incalculable.