John Calvin 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)

Whoever shall look upon a woman. Christ's design was to condemn generally the lust of the flesh. He says that not only those who have seduced their neighbors' wives, but also those who have polluted their eyes by an immodest look, are adulterers before God.

This is a synecdoche:⁴⁰⁶ for not only the eyes, but even the concealed flames of the heart, render men guilty of adultery. Accordingly, Paul makes chastity (1 Corinthians 7:34) to consist both in body and in mind.

But Christ considered it enough to refute the gross mistake that was prevalent: for they thought that it was only necessary to guard against outward adultery. Since it is generally by the lewdness of the eyes that temptations are presented to the mind, and as lust enters, as it were, by that door, Christ used this manner of speaking when he wished to condemn lust, which is evident from the expression, to lust after her.

This also teaches us that not only those who form a deliberate purpose of fornication, but also those who admit any polluted thoughts, are considered adulterers before God.

The hypocrisy of the Papists, therefore, is too gross and stupid when they affirm that lust is not a sin until it gains the full consent of the heart. But it is no wonder that they treat sin as such a small matter, for those who attribute righteousness to the merit of works must be very dull and stupid in judging their sins.

⁴⁰⁶ “C'est une facon de parler qu'on appelle Synecdoche, quand on prend une artie our le tout.” — “It is a way of speaking which is called Synecdoche, when a part is taken for the whole.”.” — “It is a way of speaking which is called Synecdoche, when a part is taken for the whole.”