Commentaria in Summam contra Gentiles, Liber III

After St. Thomas showed that man is ordered through the divine law regarding bodily things, he wishes to pursue what was his primary intent, namely to show by which precepts man is ordered to his neighbor¹. Concerning this, however, he does two things: first, he shows that man is ordered to his neighbor through certain precepts; second, he shows that those things which are commanded are also right according to nature, in the following chapter.

Concerning the first he does three things: first, he shows from the foregoing that man is ordered through the divine law to have peace and concord with his neighbor; second, by which precepts he is ordered to this²; third³, how in manifold ways he is inclined to the observance of the precepts.

I. First, he proves the first point as follows. According to the aforesaid, man is ordered through the divine law to preserve the order of reason in all things that can come into his use. Therefore it is necessary that he be directed by the divine law so that man behaves toward other men according to the order of reason. — The consequence is proved. Because among all things that come into the use of man, other men are the foremost: since man is a social animal.

Second. The end of the divine law is that man should adhere to God. But in this one man is helped by another, as much with respect to knowledge as also with respect to affection. Therefore etc. — The minor is proved. Because men help one another mutually in the knowledge of truth, and one provokes another to the good: as is shown in Prov. 27 and Eccles. 4.

Third. It belongs to divine providence to contain under due order the individual things that are subject to it: namely, that each thing hold its own order and rank. Therefore the divine law also ought so to order men that each one holds his own order. Which is for men to have peace among themselves, according to Augustine. — The consequence is proved. Because the divine law is a certain plan of divine providence for governing men.

Fourth. Whenever any things are ordered under something, it is necessary that they be harmoniously ordered toward one another: otherwise they would hinder one another in the attainment of the common end, as is evident in an army. But each man is ordered through the divine law to God. Therefore etc.

It is confirmed by the authority of the Psalm, and John 16.

It must be noted that St. Thomas takes as the same thing that man behaves toward other men according to the order of reason, and that there is ordered concord and peace among men. For reason orders one man to concord with other men, since there is one common end of all: for those things which are ordered to one common end are harmonious toward its attainment. And therefore the first argument concludes concerning the order of reason of one man toward others; while the remaining arguments conclude concerning the society and concord of men.

II. Second, St. Thomas shows the fittingness of the precepts by which man is ordered to his neighbor⁴. And he argues as follows. An ordered concord among men is preserved at that time when to each is rendered what is his own, which belongs to justice, as is said in Isaiah 32. Therefore it was necessary that precepts of justice be given through the divine law: that each one should render to each what is his own, and should abstain from inflicting harms upon him. But the precepts that order man to his neighbor are of this kind. Therefore etc.

The minor is proved. For in the precept concerning the honor of parents, set down in Exod. 20, it is understood to be commanded that each one render what he owes both to parents and to others, according to the admonition of the Apostle in Rom. 13. — But in the precepts, Thou shalt not kill, Thou shalt not commit adultery, Thou shalt not steal, it is commanded that one must abstain from inflicting harm upon one's neighbor by deeds, either in his own person; or in a conjoined person; or in external goods. Moreover, in the precept, Thou shalt not bear false witness against thy neighbor, it is forbidden that the neighbor be offended by word contrary to justice. — But because God is also the judge of hearts, we are forbidden by two other precepts from offending our neighbor even in heart, namely by coveting his wife or any other thing of his.

2. It must be noted, from the doctrine of St. Thomas, Iª II^ae, q. 100, in many articles, that although only the precepts enumerated above are set down in the Decalogue, there are nevertheless in the divine law many other moral precepts, as is evident in Deuteronomy and Leviticus. But if it be rightly considered, all have an order to the precepts of the Decalogue. For the precepts concerning the love of God and neighbor are related to them as common and self-evident principles are to conclusions: and therefore the precepts of the Decalogue are referred to these as conclusions to principles⁵. And the same must be said concerning the precept of faith: for this, which is to believe in God, is first and self-evident to one having faith⁶. But the other moral precepts that are enumerated in Sacred Scripture are reduced to the precepts of the Decalogue by way of a certain addition to them: as St. Thomas sets forth at length in the place cited above, article 11, running through each one.

III. In the third place St. Thomas shows how in manifold ways man is inclined to the observance of the precepts⁷. And he says that some are inclined to this from within: namely, when they voluntarily observe the precepts of the law through love for God and neighbor. Hence the whole fulfillment of the law depends on love: as is said in Rom. 13 and Matt. 22. Understand: because he who loves God and neighbor fulfills all the precepts of the law spontaneously and delightfully. — But some do not do what the law commands from within and spontaneously, but through fear of punishments; and they fulfill the law not freely, but servilely; which is shown in Isaiah 26.

From this St. Thomas infers that, since those who are inclined from within to the observance of the law are a law unto themselves, having charity, which inclines them in place of the law and causes them to act freely, it was not necessary that the law be set down on their account, but on account of those who are not inclined to the good from themselves. Hence in 1 Tim. 1 it is said that the law is not set down for the just man, but for the unjust: not indeed because the just are not bound to fulfill the law, but because by themselves, even without the law, they are inclined to do justice.

For the understanding of this, it must be considered, from the doctrine of St. Thomas in the place cited above⁸, that, since all moral precepts belong to the law of nature, the precepts of the Decalogue depend from the first precepts, which concern the love of God and neighbor, as immediate conclusions: and therefore they are such that they can immediately fall into the mind of any common person. But other moral precepts are not so evident to everyone, but are found through the diligent inquiry of the wise to agree with reason: and these are contained in the precepts of the Decalogue as conclusions in principles. From which it is clear that all moral precepts are in some way contained in the precepts of love. And therefore it was well said that the just are inclined from themselves, even without a compelling law, to observe justice. For from the fact that they have charity, by which they love God and neighbor, in which all precepts are virtually contained, they are inclined from charity to fulfill all precepts, even if no other law existed.

The other matters that pertain to the precepts of the Decalogue St. Thomas determines at length in the place cited above; and in IIª IIae, q. 122; and in III Sent., d. 37.