Thomas Aquinas Commentary Matthew 5:27-30

"Ye have heard that it was said, Thou shalt not commit adultery: 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. And if thy right eye causeth thee to stumble, pluck it out, and cast it from thee: for it is profitable for thee that one of thy members should perish, and not thy whole body be cast into hell. And if thy right hand causeth thee to stumble, cut it off, and cast it from thee: for it is profitable for thee that one of thy members should perish, and not thy whole body go into hell." — Matthew 5:27-30 (ASV)

You have heard that it was said to them of old: You shall not commit adultery. Above, the Lord fulfilled the Law regarding the prohibitive precept concerning murder; now He fulfills it regarding the prohibitive precept concerning adultery. And about this He does three things:

1. He sets forth the precept.
2. He sets forth the fulfillment of the precept.
3. He teaches how it can be observed.

The second part is where it is said, But I say to you, that whoever shall look on a woman; and the third part is where it is said, And if your right eye scandalize you.

And fittingly, after the prohibitive precept concerning murder, the prohibitive precept concerning adultery is discussed, because adultery holds the second place after murder. For murder is opposed to the life of an already existing man, but adultery is opposed to the life of a man yet to be born, for it takes away the certainty concerning the offspring and consequently the child's education.

You shall not commit adultery (moechaberis). Moechia is adultery properly speaking. This precept is found in Exodus 20:14 and Deuteronomy 5:18.

And it should be known that, because in the precepts of the Decalogue simple fornication is not prohibited but only adultery, some supposed that simple fornication is not a mortal sin, because it is not against the Law since it is not in the precepts of the Decalogue. Firstly, it is said in Leviticus, “If a man carnally lie with a woman… they both shall be scourged: and they shall not be put to death,” etc. (Leviticus 19:20).

Therefore, simple fornication is a venial sin. Furthermore, “All iniquity is sin. And there is a sin unto death” (1 John 5:16–17). But he who commits simple fornication commits iniquity against no one: not against himself, because he fulfills his will; nor against another person; nor against God, because it is not directly opposed to Him, as are blasphemy, idolatry, and the like. Therefore, it is not a mortal sin.

I answer that it must be most certain to the faithful that all simple fornication is a mortal sin, and, briefly, any use of the genital members outside of marriage. “For fornicators and adulterers God will judge” (Hebrews 13:4), and He presented these sins as distinct from one another, because just as He will judge adulterers, so He will judge fornicators. “Take heed to keep yourself, my son, from all fornication, and beside your wife never endure to know a crime” , and, “There shall be no whore among the daughters of Israel” (Deuteronomy 23:17). It is evident, therefore, by the authority of the Old and New Testaments, that it is a mortal sin.

And the reason for this is that marriage is natural, not only according to our faith but even to pagans. This is because it is natural that a man be joined matrimonially not to just anyone, but to one specific person, and the specific manner of celebration does not matter concerning the intention of nature. What, however, is from the natural law? Marriage is perverted in those who lack the use of reason. For the union of a man and a woman is ordained for the generation and education of children. In some animals, the female alone is sufficient for the education of the offspring, and in such animals, the father never involves himself with the education of the offspring. Thus, certainty concerning the offspring is not necessary, and consequently, such animals mate with any other, as is seen in dogs. In other animals, however, we see that the female is not able by herself to raise the offspring, and so in this case, the male and female remain together until the offspring is educated.

Therefore, it is apparent that since sexual intercourse is for the sake of education, all sexual intercourse from which the due education does not follow is against nature. Therefore, since a newborn child needs many things from the father’s care, it is necessary that the man have a specific woman, and this is marriage. Now, whether a man may have many women is another question. Therefore, fornication will be opposed to this education. Consequently, it is against nature and a mortal sin.

Now Moses spoke to the Jews, as a teacher to an ignorant audience, giving the most basic principles. The Decalogue is the beginning of the Law, and thus it expresses in it only those principles that are most evident. Hence, some say that God Himself spoke the Decalogue, leaving all other things to be explained by others. Hence, in these words, You shall not commit adultery, every other sin arising from the use of the genital members outside of marriage is understood.

Likewise, the fornicator sins against himself: “He that commits fornication sins against his own body” (1 Corinthians 6:18), because acts of this kind should not be done except for the generation of another. Likewise, under the Law, certain sins were not punished by death, such as theft and many other sins; therefore, the objection from Leviticus proves nothing. Therefore, it is evident that fornication is a mortal sin.

But I say to you, that whoever shall look on a woman to lust after her. Here the Lord fulfills the Law regarding the prohibitive precept concerning adultery. For the Pharisees and scribes understood this precept, You shall not commit adultery, only concerning the act of adultery. Now the Lord also forbids concupiscence. But here Augustine objects that the prohibition of concupiscence is a precept of the Decalogue: “You shall not covet your neighbor’s wife: nor his house, nor his field, nor his manservant, nor his maidservant, nor his ox, nor his ass, nor any thing that is his” (Deuteronomy 5:21). Therefore, the Lord did not fulfill this precept of the Law. And he replies that the Lord understands “You shall not covet your neighbor’s wife” as taking away [all related sins]; hence, He puts You shall not commit adultery together with “You shall not covet your neighbor’s wife… nor his maidservant.”

And observe that He does not say, ‘He who looks and lusts,’ but who shall look on a woman to lust after her. And it is explained in two ways. Firstly, it is explained as follows.

He who shall look on a woman to lust after her, meaning, with the purpose of lusting, so that there is concomitance. There are two kinds of concupiscence: one which is a propassion and the other is a passion. Something is called a propassion, so to speak, an imperfect passion, when the movement exists merely in the sensible appetite without the consent of reason. Something is called a passion when reason consents to the movement in the sensible appetite, and then it is a mortal sin. And thus, He says, He has already committed adultery with her in his heart, because God is the searcher of hearts, and such a man does not forgo the act except because of an obstacle.

Or, the word to, according to Augustine, conveys an end, meaning, he who shall look on a woman to lust after her, that is to say, for the very purpose that he may lust. But the rule is that whatever a man does for the sake of a mortal sin is all a mortal sin, and whatever he does for the sake of a meritorious end is all meritorious, as is evident in the case of a man who goes out to church or goes out to steal: whatever happens in the meantime, all is either meritorious or a sin. Now there are two kinds of consent. One is consent to the act, as when reason proceeds in that it wants to do the act for the sake of a final end.

The other is consent to pleasure, as when one stirs up shameful pleasures in order to enjoy them. Although one does not consent in the first manner, it is a mortal sin when a man looks upon a woman for the purpose of taking shameful pleasure, and therefore he has consented, already having committed adultery in his heart as far as God is concerned. “I made a covenant with my eyes, that I would not so much as think upon a virgin” (Job 31:1), and, “Gaze not upon a maiden, lest her beauty be a stumbling block to you” .

Chrysostom also says that women who adorn themselves for the purpose of being lusted after sin mortally: “If a man open a pit, and dig one, and cover it not, and an ox or an ass fall into it, the owner of the pit shall pay the price of the beasts” (Exodus 21:33). And if no one lusts after her, nonetheless it should be said that she sins mortally, just as does one who prepares poison. For although it is not taken by him for whom it is prepared, nevertheless she, by preparing it, sins mortally, because, as far as it is in her power, she has killed.

And if your right eye scandalize you. Here the Lord shows how this precept can be easily observed, namely as follows: by avoiding occasions of sin. Now occasions of sin are designated by the eye and the hand for four reasons. Firstly, the eye and the hand are corporeal, and so cut it off should be understood corporeally.

According to Chrysostom, this explanation cannot stand, because there is no member of the body that may not scandalize; “For I know that there dwells not in me, that is to say, in my flesh, that which is good” (Romans 7:18). Hence, all the members of the body would need to be cut off. Therefore, this is not the meaning here.

Or it is otherwise. For the body is said to be killed in two ways: as regards the life of its nature and by guilt. “Our old man is crucified with him, that the body of sin may be destroyed, to the end that we may serve sin no longer” (Romans 6:6). And so, cut off your right eye to sin. But the left eye would not then be innocent. Therefore, this is not the meaning here.

I reply, therefore, that the eye sometimes signifies a neighbor who is a help to you, for the function of the eye is to direct you on your way. Hence, your counselor in worldly matters is your left eye, and your counselor in divine matters is your right eye. The function of the hand is that it helps you. Hence, a neighbor who assists in temporal matters is your left hand, and in spiritual matters, your right hand; “I was an eye to the blind, and a foot to the lame” (Job 29:15). Therefore, understanding this passage according to this meaning, the eye or hand may scandalize you in two ways. For if some counselor in worldly or divine matters scandalizes you, cut it off, etc. He does not mention the left one, because if the right one should be cut off, all the more should the left one be cut off, etc.

Or it is otherwise. The Lord wants you not only to guard purity in yourself but also in your family; hence, if an unclean person lives in your family, cut off, etc., that person; “He that works pride shall not dwell in the midst of my house” (Psalms 100:7).

Or we can understand the eye or hand as referring to the inner man. “Though our outward man is corrupted, yet the inward man is renewed day by day” (2 Corinthians 4:16), because as the exterior man is, so is the interior. “May God give unto you enlightened eyes of your heart” (Ephesians 1:17–18). Now in this passage, the motive power is called the hand and the intellectual power is called the eye. According to this, the passage can be explained in two ways.

Firstly, it is as follows. From the fact that man’s inner eye (which is in his intellectual part that has free will) is on his right side, and his exterior eye [which is in his sensible part that does not have free will] is on his left, the Lord does not say that you should cut off your left part. This is because it is not in the power of free will to prevent the exterior members from being moved, but rather to prevent the inner members from being moved wrongly and from looking wrongly. He says, therefore, And if your right eye scandalize you, if it leads to thinking badly, remove this understanding; likewise, if the will is bad, remove it.

Or it is otherwise. The eye designates a good intention, and the hand designates a good desire; if scandal or an occasion of concupiscence were to follow from these, remove it, etc. For example, if one has a good desire in visiting poor women, and if an occasion of concupiscence were to follow from this, cut it off.

Fourthly, by the eye, the contemplative life can be signified; by the hand, the active life can be signified. These things sometimes scandalize, because sometimes error occurs from excessive contemplation. Likewise, someone, because he is not suited for it, does not fulfill the work of contemplation but degenerates into laziness; “The enemies have seen her, and have mocked at her sabbaths” (Lamentations 1:7). Therefore, cut it off and turn to a practice of labor. Or, in the active life, people sometimes become troubled and run into occasions of sin; hence, one should move to a different state.

Therefore, the first manner of explaining should be excluded; the second manner concerns one's neighbor; the third manner concerns the inner man; the fourth manner concerns a good intention and a good work; and in the fifth manner, the passage is explained as concerning the active and contemplative life, where they explain the passage, For it is expedient for you that one of your members should perish, etc.