Calvin's Commentaries, Vol. 31: Matthew, Mark and Luke, Part I, tr. by John King, [1847-50], at sacred-texts.com
27. You have heard that it was said to the ancients, Thou shalt not commit adultery. 28. But I say to you, That whoever shall look upon a woman to lust after her, hath already committed adultery with her in his heart. 29. And if thy right eye shall be a stumbling block 405 to thee, pluck it out, and cast it from thee: for it is better for thee that one of thy members perish, and that thy whole body be not thrown into hell. 30. And if thy right hand shall be a hindrance to thee, cut it off, and cast it from thee: for it is better that one of thy members perish, and that thy whole body be not thrown into hell.
Matthew 5:27. Thou shalt not commit adultery. Christ proceeds with his subject, and shows, that the law of God not only has authority over the life, in a political view, to form the outward manners, but that it requires pure and holy affections of the heart. We must remember what I have already stated, that though Christ quotes the very words of the law, it is the gross and false meaning, which had been put upon it by dishonest interpreters, that he blames. He has already told us, that he did not come as a new Legislator, but as the faithful expounder of a law which had been already given. It might be objected that, through long practice, that interpretation had grown old. Christ expressly admits this, but meets it by saying, that the antiquity of an error ought not to be allowed to plead in its favor.
28. Whoever shall look upon a woman. The design of Christ was to condemn generally the lust of the flesh. He says, that not only those who have seduced their neighbors’ wives, but those who have polluted their eyes by an immodest look, are adulterers before God. This is a synec-doche: 406 for not only the eyes, but even the concealed flames of the heart, render men guilty of adultery. Accordingly, Paul makes chastity (1Co 7:34) to consist both in body and in mind. But Christ reckoned it enough to refute the gross mistake which was prevalent: for they thought that it was only necessary to guard against outward adultery. As it is generally by the wantonness of the eyes that temptations are presented to the mind, and as lust enters, as it were, by that door, Christ used this mode of speaking, when he wished to condemn lust: which is evident from the expression, to lust after her. This teaches us also, that not only those who form a deliberate purpose of fornication, but those who admit any polluted thoughts, are reckoned 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 gain the full consent of the heart. But we need not wonder, that they make sin to be so small a matter: for those who ascribe righteousness to the merit of works must be very dull and stupid in judging of their sins.
29. If thy right eye shall be a stumbling-block to thee. It might be thought that, considering the weakness of the flesh and of nature, Christ pressed too severely on men, and therefore he anticipates all such complaints. The general meaning is, that however difficult, or severe, or troublesome, or harsh, any commandment of God may be, yet no excuse ought to be pleaded on those grounds, because the justice of God ought to stand higher in our estimation, than all that we reckon most precious and valuable. “You have no right to object to me, that you can scarcely turn your eyes in any direction, without being suddenly drawn away by some temptation: for you ought rather to part with your eyes, than to depart from the commandments of God.” And yet Christ does not mean, that we must mutilate our body, in order to obey God: but as all would readily wish, that they should not be restrained from the free use of their senses, Christ employs an exaggerated 407 form of speech to show, that whatever hinders us from yielding that obedience to God which he requires in his law, ought to be cut off. And he does so expressly, because men allow themselves too much liberty in that respect. If the mind were pure, the eyes and hands would be obedient to it; for it is certain, that they have no movement of their own. But here we are deeply to blame. We are so far from being as careful as we ought to be, to avoid allurements, that we rather provoke our senses to wickedness by allowing them unbounded liberty.
“Si ton ceil dextre to fait chopper.” — “If thy right eye makes thee stumble.”
“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.”
“Par une facon de parler hyperbolique, (c’est a dire, excessive:”) — “by a hyperbolical, that is, an excessive mode of speaking.”