Charles Ellicott Commentary Matthew 5:28

"but I say unto you, that every one that looketh on a woman to lust after her hath committed adultery with her already in his heart." — Matthew 5:28 (ASV)

To lust after her — The intent is more strongly marked in the Greek than in the English. It is not the passing glance or even the momentary impulse of desire, but the continued gaze by which the impulse is deliberately cherished until it becomes a passion.

It has often been remarked, and in a disparaging way, that this noble and beautiful teaching is found elsewhere. Such criticism, however, is out of place. By the mercy of God, the Light that lighteth every man has led people to recognize the truth asserted here. Parallels to it may be found in the writings of Confucius, Seneca, Epictetus, and even of the Jewish Rabbis themselves. The words of Juvenal closely express the general sentiment:

Scelus intra se tacitus qui cogitat ullum,
Facti crimen habet.

[Who in his breast a guilty thought cherishes,
He bears the guilt of action.]

Our Lord’s words speak primarily of adultery, but are, of course, applicable to every form of sensual impurity.