As to the precepts that direct man in his behavior towards his neighbor, it is evident that it is more repugnant to reason, and a more grievous sin, if man does not observe the due order as to those persons to whom he is most indebted. Consequently, among those precepts that direct man in his relations to his neighbor, the first place is given to that one which regards his parents. Among the other precepts we again find the order to be according to the gravity of sin. For it is more grave and more repugnant to reason, to sin by deed than by word; and by word than by thought. And among sins of deed, murder which destroys life in one already living is more grievous than adultery, which imperils the life of the unborn child; and adultery is more grave than theft, which regards external goods.
Reply Obj. 1: Although our neighbor is better known than God by the way of the senses, nevertheless the love of God is the reason for the love of our neighbor, as shall be declared later on (II-II, Q. 25, A. 1; Q. 26, A. 2). Hence the precepts ordaining man to God demanded precedence of the others.
Reply Obj. 2: Just as God is the universal principle of being in respect of all things, so is a father a principle of being in respect of his son. Therefore the precept regarding parents was fittingly placed after the precepts regarding God. This argument holds in respect of affirmative and negative precepts about the same kind of deed: although even then it is not altogether cogent. For although in the order of execution, vices should be uprooted before virtues are sown, according to Ps. 33:15: "Turn away from evil, and do good," and Isa. 1:16, 17: "Cease to do perversely; learn to do well"; yet, in the order of knowledge, virtue precedes vice, because "the crooked line is known by the straight" (De Anima i): and "by the law is the knowledge of sin" (Rom. 3:20). Wherefore the affirmative precept demanded the first place. However, this is not the reason for the order, but that which is given above. Because in the precepts regarding God, which belongs to the first table, an affirmative precept is placed last, since its transgression implies a less grievous sin.
Reply Obj. 3: Although sin of thought stands first in the order of execution, yet its prohibition holds a later position in the order of reason. ________________________
SEVENTH ARTICLE [I-II, Q. 100, Art. 7]
Whether the Precepts of the Decalogue Are Suitably Formulated?
Objection 1: It would seem that the precepts of the decalogue are unsuitably formulated. Because the affirmative precepts direct man to acts of virtue, while the negative precepts withdraw him from acts of vice. But in every matter there are virtues and vices opposed to one another. Therefore in whatever matter there is an ordinance of a precept of the decalogue, there should have been an affirmative and a negative precept. Therefore it was unfitting that affirmative precepts should be framed in some matters, and negative precepts in others.
Obj. 2: Further, Isidore says (Etym. ii, 10) that every law is based on reason. But all the precepts of the decalogue belong to the Divine law. Therefore the reason should have been pointed out in each precept, and not only in the first and third.
Obj. 3: Further, by observing the precepts man deserves to be rewarded by God. But the Divine promises concern the rewards of the precepts. Therefore the promise should have been included in each precept, and not only in the second and fourth.
Obj. 4: Further, the Old Law is called "the law of fear," in so far as it induced men to observe the precepts, by means of the threat of punishments. But all the precepts of the decalogue belong to the Old Law. Therefore a threat of punishment should have been included in each, and not only in the first and second.