Proverbs 24:29

Say not, I will do so to him as he hath done to me: I will render to the man according to his work.

Personal revenge is forbidden by barring anyone from repaying another person with the same evil that person has done. The requirement of equal punishment for injury was a civil statute for public justice, not permission for individuals to avenge themselves. Instead of taking revenge, recompense is to be left to the Lord while showing kindness to an enemy.