Matthew 5:27,28

Ver 27. "Ye have heard that it was said by them of old time, 'Thou shalt not commit adultery:' 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."

Chrys., Hom. xvii: The Lord having explained how much is contained in the first commandment, namely, "Thou shalt not kill," proceeds in regular order to the second.

Aug., Serm. ix, 3 and 10: "Thou shalt not commit adultery," that is, Thou shalt go no where but to thy lawful wife. For if you exact this of your wife, you ought to do the same, for the husband ought to go before the wife in virtue. It is a shame for the husband to say that this is impossible. Why not the husband as well as the wife? And let not him that is unmarried suppose that he does not break this commandment by fornication; you know the price wherewith you have been bought, you know what you eat and what your drink [ed. note, g: Nic. inserts here, from the original, 'immo quem manduces, quem bibas.'] therefore keep yourself from fornications. Forasmuch as all such acts of lust pollute and destroy God's image, (which you are,) the Lord who knows what is good for you, gives you this precept that you may not pull down His temple which you have begun to be.

Aug., cont. Faust. 19, 23: He then goes on to correct the error of the Pharisees, declaring, "Whoso looketh upon a woman to lust after her, hath committed adultery already with her in his heart." For the commandment of the Law, "Thou shalt not lust after thy neighbour's wife," [Exodus 20:17] the Jews understood of taking her away, not of committing adultery with her.

Jerome: Between and that is between actual passion and the first spontaneous movement of the mind, there is this difference: passion is at once a sin; the spontaneous movement of the mind, though it partakes of the evil of sin, is yet not held for an offence committed. [ed. note, h: In this passage S. Jerome, who seems to have introduced the word propassio, into theology, uses it somewhat in a sense of his own; viz. as involving something of the nature of sin; vid. also Comm. in Ezek. xviii, 1, 2. The word is more commonly applied to our Lord, as denoting the mode and extent in which His soul was affected by what in others became. In us passion precedes reason, in Him it followed, or was a. vid. S. Jerome in Matt. xxvi. 37. Leon. Ep. 35. Damasc. F. O. iii. 20 &c. &c.]

When then one looks upon a woman, and his mind is therewith smitten, there is propassion; if he yields to this he passes from propassion to passion, and then it is no longer the will but the opportunity to sin that is wanting. "Whosoever," then, "looketh on a woman to lust after her," that is, so looks on her as to lust, and cast about to obtain, he is rightly said to commit adultery with her in his heart.

Aug., Serm. in Mont., i, 12: For there are three things which make up a sin; suggestion either through the memory, or the present sense; if the thought of the pleasure of indulgence follows, that is an unlawful thought, and to be restrained; if you consent then, the sin is complete. For prior to the first consent, the pleasure is either none or very slight, the consenting to which makes the sin. But if consent proceeds on into overt act, then desire seems to be satiated and quenched. And when suggestion is again repeated, the contemplated pleasure is greater, which previous to habit formed was but small, but now more difficult to overcome.

Greg., Mor., xxi, 2: But whoso casts his eyes about without caution will often be taken with the pleasure of sin, and ensnared by desires begins to wish for what he would not. Great is the strength of the flesh to draw us downwards, and the charm of beauty once admitted to the heart through the eye, is hardly banished by endeavour. We must therefore take heed at the first, we ought not to look upon what it is unlawful to desire. For that the heart may be kept pure in thought, the eyes, as being on the watch to hurry us to sin, should be averted from wanton looks.

Chrys.: If you permit yourself to gaze often on fair countenances you will assuredly be taken, even though you may be able to command your mind twice or thrice. For you are not exalted above nature and the strength of humanity. She too who dresses and adorns herself for the purpose of attracting men's eyes to her, though her endeavor should fail, yet shall she be punished hereafter; seeing she mixed the poison and offered the cup, though none was found who would drink thereof. For what the Lord seems to speak only to the man, is of equal application to the woman; inasmuch as when He speaks to the head, the warning is meant for the whole body.