Adam Clarke on Matthew 5:38

An eye for an eye - Our Lord refers here to the law of retaliation mentioned See Exo 21:24, (see the note there, and see Lev 24:20 (note)), which obliged the offender to suffer the same injury he had committed. The Greeks and Romans had the same law. So strictly was it attended to at Athens, that if a man put out the eye of another who had but one, the offender was condemned to lose both his eyes, as the loss of one would not be an equivalent misfortune. It seems that the Jews had made this law (the execution of which belonged to the civil magistrate) a ground for authorizing private resentments, and all the excesses committed by a vindictive spirit. Revenge was often carried to the utmost extremity, and more evil returned than what had been received. This is often the case among those who are called Christians.