Jerome
Catena Aurea · Matthäusevangelium 5
Ye have heard that it was said by them of old time, Thou shalt not commit adultery: But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.
Between πάθος and προπάθεια, 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 committedh. 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.