Matthew 5:28

But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.

The Sixth Commandment had indeed been given to "them of old time," Exodus 20:14; Deuteronomy 5:18. But it was understood by the Jewish teachers of the sin in deed only, of the deliberate unfaithfulness of those joined in wedlock, or the carnal intercourse of the unmarried. Many rabbis expressly stated that the evil thought should not be regarded on a level with the sinful act. Christ's explanation opens the deeper meaning of the commandment. He finds the beginning of adultery in the deliberate nourishing of the awakening lust of the heart. A woman may be seen, come within the range of vision of a man, and there is no wrong in the act. Ordinary human intercourse would be impossible without it. But when the look turned upon any woman, married or unmarried, is deliberate and intentional, conscious and persistent, as on a person of the opposite sex, and this is followed by an impure desire of coveting her for immoral purposes, then adultery has in fact been committed, although the sin is hidden deeply in the heart.