Jamieson, Fausset and Brown on Matthew 5:39

39. But I say unto you, That ye resist not evil; but whosoever shall smite thee on thy right check, turn to him the other also--Our Lord's own meek, yet dignified bearing, when smitten rudely on the cheek (Joh 18:22, 23), and not literally presenting the other, is the best comment on these words. It is the preparedness, after one indignity, not to invite but to submit meekly to another, without retaliation, which this strong language is meant to convey.