Objection 2: Further, every law is directed to the end which the lawgiver intends for those for whom he makes the law. But God intends one and the same thing for all men; since according to 1 Tim. 2:4 : "He will have all men to be saved, and to come to the knowledge of the truth." Therefore there is but one Divine law.
Objection 3: Further, the Divine law seems to be more akin to the eternal law, which is one, than the natural law, according as the revelation of grace is of a higher order than natural knowledge. Therefore much more is the Divine law but one.
On the contrary, The Apostle says ( Heb. 7:12 ): "The priesthood being translated, it is necessary that a translation also be made of the law." But the priesthood is twofold, as stated in the same passage, viz. the levitical priesthood, and the priesthood of Christ. Therefore the Divine law is twofold, namely the Old Law and the New Law.
I answer that, As stated in the FP, Q[30], A[3], distinction is the cause of number. Now things may be distinguished in two ways. First, as those things that are altogether specifically different, e.g. a horse and an ox. Secondly, as perfect and imperfect in the same species, e.g. a boy and a man: and in this way the Divine law is divided into Old and New. Hence the Apostle ( Gal. 3:24 , 25 ) compares the state of man under the Old Law to that of a child "under a pedagogue"; but the state under the New Law, to that of a full grown man, who is "no longer under a pedagogue."
Now the perfection and imperfection of these two laws is to be taken in connection with the three conditions pertaining to law, as stated above. For, in the first place, it belongs to law to be directed to the common good as to its end, as stated above (Q[90], A[2]). This good may be twofold. It may be a sensible and earthly good; and to this, man was directly ordained by the Old Law: wherefore, at the very outset of the law, the people were invited to the earthly kingdom of the Chananaeans ( Exod. 3:8 , 17 ). Again it may be an intelligible and heavenly good: and to this, man is ordained by the New Law. Wherefore, at the very beginning of His preaching, Christ invited men to the kingdom of heaven, saying ( Mat. 4:17 ): "Do penance, for the kingdom of heaven is at hand." Hence Augustine says (Contra Faust. iv) that "promises of temporal goods are contained in the Old Testament, for which reason it is called old; but the promise of eternal life belongs to the New Testament."
Secondly, it belongs to the law to direct human acts according to the order of righteousness (A[4]): wherein also the New Law surpasses the Old Law, since it directs our internal acts, according to Mat. 5:20 : "Unless your justice abound more than that of the Scribes and Pharisees, you shall not enter into the kingdom of heaven." Hence the saying that "the Old Law restrains the hand, but the New Law controls the mind" ( Sentent. iii, D, xl).
Thirdly, it belongs to the law to induce men to observe its commandments. This the Old Law did by the fear of punishment: but the New Law, by love, which is poured into our hearts by the grace of Christ, bestowed in the New Law, but foreshadowed in the Old. Hence Augustine says (Contra Adimant. Manich. discip. xvii) that "there is little difference [*The 'little difference' refers to the Latin words 'timor' and 'amor'---'fear' and 'love.'] between the Law and the Gospel---fear and love."
Reply to Objection 1: As the father of a family issues different commands to the children and to the adults, so also the one King, God, in His one kingdom, gave one law to men, while they were yet imperfect, and another more perfect law, when, by the preceding law, they had been led to a greater capacity for Divine things.
Reply to Objection 2: The salvation of man could not be achieved otherwise than through Christ, according to Acts 4:12 : "There is no other name . . . given to men, whereby we must be saved." Consequently the law that brings all to salvation could not be given until after the coming of Christ. But before His coming it was necessary to give to the people, of whom Christ was to be born, a law containing certain rudiments of righteousness unto salvation, in order to prepare them to receive Him.
Reply to Objection 3: The natural law directs man by way of certain general precepts, common to both the perfect and the imperfect: wherefore it is one and the same for all. But the Divine law directs man also in certain particular matters, to which the perfect and imperfect do not stand in the same relation. Hence the necessity for the Divine law to be twofold, as already explained.
Whether there is a law in the fomes of sin?
Objection 1: It would seem that there is no law of the "fomes" of sin. For Isidore says (Etym. v) that the "law is based on reason." But the "fomes" of sin is not based on reason, but deviates from it. Therefore the "fomes" has not the nature of a law.
Objection 2: Further, every law is binding, so that those who do not obey it are called transgressors. But man is not called a transgressor, from not following the instigations of the "fomes"; but rather from his following them. Therefore the "fomes" has not the nature of a law.
Objection 3: Further, the law is ordained to the common good, as stated above (Q[90], A[2]). But the "fomes" inclines us, not to the common, but to our own private good. Therefore the "fomes" has not the nature of sin.
On the contrary, The Apostle says ( Rom. 7:23 ): "I see another law in my members, fighting against the law of my mind."
I answer that, As stated above (A[2]; Q[90], A[1], ad 1), the law, as to its essence, resides in him that rules and measures; but, by way of participation, in that which is ruled and measured; so that every inclination or ordination which may be found in things subject to the law, is called a law by participation, as stated above (A[2]; Q[90], A[1] , ad 1). Now those who are subject to a law may receive a twofold inclination from the lawgiver. First, in so far as he directly inclines his subjects to something; sometimes indeed different subjects to different acts; in this way we may say that there is a military law and a mercantile law. Secondly, indirectly; thus by the very fact that a lawgiver deprives a subject of some dignity, the latter passes into another order, so as to be under another law, as it were: thus if a soldier be turned out of the army, he becomes a subject of rural or of mercantile legislation.
Accordingly under the Divine Lawgiver various creatures have various natural inclinations, so that what is, as it were, a law for one, is against the law for another: thus I might say that fierceness is, in a way, the law of a dog, but against the law of a sheep or another meek animal. And so the law of man, which, by the Divine ordinance, is allotted to him, according to his proper natural condition, is that he should act in accordance with reason: and this law was so effective in the primitive state, that nothing either beside or against reason could take man unawares. But when man turned his back on God, he fell under the influence of his sensual impulses: in fact this happens to each one individually, the more he deviates from the path of reason, so that, after a fashion, he is likened to the beasts that are led by the impulse of sensuality, according to Ps. 48:21 : "Man, when he was in honor, did not understand: he hath been compared to senseless beasts, and made like to them."
So, then, this very inclination of sensuality which is called the "fomes," in other animals has simply the nature of a law (yet only in so far as a law may be said to be in such things), by reason of a direct inclination. But in man, it has not the nature of law in this way, rather is it a deviation from the law of reason. But since, by the just sentence of God, man is destitute of original justice, and his reason bereft of its vigor, this impulse of sensuality, whereby he is led, in so far as it is a penalty following from the Divine law depriving man of his proper dignity, has the nature of a law.
Reply to Objection 1: This argument considers the "fomes" in itself, as an incentive to evil. It is not thus that it has the nature of a law, as stated above, but according as it results from the justice of the Divine law: it is as though we were to say that the law allows a nobleman to be condemned to hard labor for some misdeed.
Reply to Objection 2: This argument considers law in the light of a rule or measure: for it is in this sense that those who deviate from the law become transgressors. But the "fomes" is not a law in this respect, but by a kind of participation, as stated above.
Reply to Objection 3: This argument considers the "fomes" as to its proper inclination, and not as to its origin. And yet if the inclination of sensuality be considered as it is in other animals, thus it is ordained to the common good, namely, to the preservation of nature in the species or in the individual. And this is in man also, in so far as sensuality is subject to reason. But it is called "fomes" in so far as it strays from the order of reason.