39 But I say unto you, That ye resist not evil: but whosoever shall smite thee on thy right cheek, turn to him the other also.
Two things are addressed over here. First, an eye for an eye was meant as a legal principle, meaning that punishment had to be proportional to the crime committed (not an eye for a tooth or a life for an eye), it was not meant to be taken literally neither was it to be used as a license to personal revenge, yet that's exactly how it had been interpreted by some people in those times.
Second, slapping some on his cheek is an insult, not an assault, though nowadays it's viewed as one. After all, the Scriptures don't say: "And whosoever rapeth thine wife, give him thine daughter also", do they? Another unfortunate tendency of those times was to start law suits at the slightest provocation including small personal insults which could best be forgotten. The very next verse deals with it, warning against litigiousness.
Since our society is increasingly pacifistic, feminised and liberal it's probably difficult for us to understand that not so very long ago, it was normal in some cultures to start feuds about most trivial things. While I'm sure that this verse is not to be taken literally (after all, Jesus himself didn't turn the other cheek but rather confronted the one who hit him, cf. John 18: 22, 23) I'd like to give an example involving exactly the same situation described in the verse.
In Njals saga beautiful Hallgerðr refuses to help her husband when his life is at stake, because he had once slapped her (after being thoroughly provoked, as far as I can remember), which leads to his death. In fact, it becomes extremely difficult to maintain a form of civilisation when all the citizens are either busy running to the courts because someone somewhere may have hurt their feelings, or cutting each other's throats for the slightest offence. And that, imho, is the real meaning of the verse.
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