Summa Th. I-II EN Qu.96 a.5

Whether all are subject to the law?


Objection: 1. It would seem that not all are subject to the law. For those alone are subject to a law for whom a law is made. But the Apostle says (
1Tm 1,9): "The law is not made for the just man." Therefore the just are not subject to the law.
2. Further, Pope Urban says [*Decretals. caus. xix, qu. 2]: "He that is guided by a private law need not for any reason be bound by the public law." Now all spiritual men are led by the private law of the Holy Ghost, for they are the sons of God, of whom it is said (Rm 8,14): "Whosoever are led by the Spirit of God, they are the sons of God." Therefore not all men are subject to human law.
3. Further, the jurist says [*Pandect. Justin. i, ff., tit. 3, De Leg. et Senat.] that "the sovereign is exempt from the laws." But he that is exempt from the law is not bound thereby. Therefore not all are subject to the law.

On the contrary
The Apostle says (Rm 13,1): "Let every soul be subject to the higher powers." But subjection to a power seems to imply subjection to the laws framed by that power. Therefore all men should be subject to human law.
I answer that As stated above (Question [90], Articles [1],2; Article [3], ad 2), the notion of law contains two things: First, that it is a rule of human acts; secondly, that it has coercive power. Wherefore a man may be subject to law in two ways. First, as the regulated is subject to the regulator: and, in this way, whoever is subject to a power, is subject to the law framed by that power. But it may happen in two ways that one is not subject to a power. In one way, by being altogether free from its authority: hence the subjects of one city or kingdom are not bound by the laws of the sovereign of another city or kingdom, since they are not subject to his authority. In another way, by being under a yet higher law; thus the subject of a proconsul should be ruled by his command, but not in those matters in which the subject receives his orders from the emperor: for in these matters, he is not bound by the mandate of the lower authority, since he is directed by that of a higher. In this way, one who is simply subject to a law, may not be a subject thereto in certain matters, in respect of which he is ruled by a higher law.Secondly, a man is said to be subject to a law as the coerced is subject to the coercer. In this way the virtuous and righteous are not subject to the law, but only the wicked. Because coercion and violence are contrary to the will: but the will of the good is in harmony with the law, whereas the will of the wicked is discordant from it. Wherefore in this sense the good are not subject to the law, but only the wicked.

Reply to Objection: 1.
This argument is true of subjection by way of coercion: for, in this way, "the law is not made for the just men": because "they are a law to themselves," since they "show the work of the law written in their hearts," as the Apostle says (Rm 2,14-15). Consequently the law does not enforce itself upon them as it does on the wicked.
2. The law of the Holy Ghost is above all law framed by man: and therefore spiritual men, in so far as they are led by the law of the Holy Ghost, are not subject to the law in those matters that are inconsistent with the guidance of the Holy Ghost. Nevertheless the very fact that spiritual men are subject to law, is due to the leading of the Holy Ghost, according to 1P 2,13: "Be ye subject . . . to every human creature for God's sake."
3. The sovereign is said to be "exempt from the law," as to its coercive power; since, properly speaking, no man is coerced by himself, and law has no coercive power save from the authority of the sovereign. Thus then is the sovereign said to be exempt from the law, because none is competent to pass sentence on him, if he acts against the law. Wherefore on Ps 50,6: "To Thee only have I sinned," a gloss says that "there is no man who can judge the deeds of a king." But as to the directive force of law, the sovereign is subject to the law by his own will, according to the statement (Extra, De Constit. cap. Cum omnes) that "whatever law a man makes for another, he should keep himself. And a wise authority [*Dionysius Cato, Dist. de Moribus] says: 'Obey the law that thou makest thyself.'" Moreover the Lord reproaches those who "say and do not"; and who "bind heavy burdens and lay them on men's shoulders, but with a finger of their own they will not move them" (Mt 23,3-4). Hence, in the judgment of God, the sovereign is not exempt from the law, as to its directive force; but he should fulfil it to his own free-will and not of constraint. Again the sovereign is above the law, in so far as, when it is expedient, he can change the law, and dispense in it according to time and place.

Whether he who is under a law may act beside the letter of the law?


Objection: 1. It seems that he who is subject to a law may not act beside the letter of the law. For Augustine says (De Vera Relig. 31): "Although men judge about temporal laws when they make them, yet when once they are made they must pass judgment not on them, but according to them." But if anyone disregard the letter of the law, saying that he observes the intention of the lawgiver, he seems to pass judgment on the law. Therefore it is not right for one who is under the law to disregard the letter of the law, in order to observe the intention of the lawgiver.
Further, he alone is competent to interpret the law who can make the law. But those who are subject to the law cannot make the law. Therefore they have no right to interpret the intention of the lawgiver, but should always act according to the letter of the law.
Further, every wise man knows how to explain his intention by words. But those who framed the laws should be reckoned wise: for Wisdom says (Pr 8,15): "By Me kings reign, and lawgivers decree just things." Therefore we should not judge of the intention of the lawgiver otherwise than by the words of the law.

On the contrary Hilary says (De Trin. iv): "The meaning of what is said is according to the motive for saying it: because things are not subject to speech, but speech to things." Therefore we should take account of the motive of the lawgiver, rather than of his very words.
I answer that
As stated above (Article [4]), every law is directed to the common weal of men, and derives the force and nature of law accordingly. Hence the jurist says [*Pandect. Justin. lib. i, ff., tit. 3, De Leg. et Senat.]: "By no reason of law, or favor of equity, is it allowable for us to interpret harshly, and render burdensome, those useful measures which have been enacted for the welfare of man." Now it happens often that the observance of some point of law conduces to the common weal in the majority of instances, and yet, in some cases, is very hurtful. Since then the lawgiver cannot have in view every single case, he shapes the law according to what happens most frequently, by directing his attention to the common good. Wherefore if a case arise wherein the observance of that law would be hurtful to the general welfare, it should not be observed. For instance, suppose that in a besieged city it be an established law that the gates of the city are to be kept closed, this is good for public welfare as a general rule: but, it were to happen that the enemy are in pursuit of certain citizens, who are defenders of the city, it would be a great loss to the city, if the gates were not opened to them: and so in that case the gates ought to be opened, contrary to the letter of the law, in order to maintain the common weal, which the lawgiver had in view.Nevertheless it must be noted, that if the observance of the law according to the letter does not involve any sudden risk needing instant remedy, it is not competent for everyone to expound what is useful and what is not useful to the state: those alone can do this who are in authority, and who, on account of such like cases, have the power to dispense from the laws. If, however, the peril be so sudden as not to allow of the delay involved by referring the matter to authority, the mere necessity brings with it a dispensation, since necessity knows no law.

Reply to Objection: 1.
He who in a case of necessity acts beside the letter of the law, does not judge the law; but of a particular case in which he sees that the letter of the law is not to be observed.
He who follows the intention of the lawgiver, does not interpret the law simply; but in a case in which it is evident, by reason of the manifest harm, that the lawgiver intended otherwise. For if it be a matter of doubt, he must either act according to the letter of the law, or consult those in power.
No man is so wise as to be able to take account of every single case; wherefore he is not able sufficiently to express in words all those things that are suitable for the end he has in view. And even if a lawgiver were able to take all the cases into consideration, he ought not to mention them all, in order to avoid confusion: but should frame the law according to that which is of most common occurrence.



We must now consider change in laws: under which head there are four points of inquiry:

(1) Whether human law is changeable?

(2) Whether it should be always changed, whenever anything better occurs?

(3) Whether it is abolished by custom, and whether custom obtains the force of law?

(4) Whether the application of human law should be changed by dispensation of those in authority?

Whether human law should be changed in any way?


Objection: 1. It would seem that human law should not be changed in any way at all. Because human law is derived from the natural law, as stated above (Question [95], Article [2]). But the natural law endures unchangeably. Therefore human law should also remain without any change.
Further, as the Philosopher says (Ethic. v, 5), a measure should be absolutely stable. But human law is the measure of human acts, as stated above (Question [90], Articles [1],2). Therefore it should remain without change.
Further, it is of the essence of law to be just and right, as stated above (Question [95], Article [2]). But that which is right once is right always. Therefore that which is law once, should be always law.

On the contrary
Augustine says (De Lib. Arb. i, 6): "A temporal law, however just, may be justly changed in course of time."
I answer that
As stated above (Question [91], Article [3]), human law is a dictate of reason, whereby human acts are directed. Thus there may be two causes for the just change of human law: one on the part of reason; the other on the part of man whose acts are regulated by law. The cause on the part of reason is that it seems natural to human reason to advance gradually from the imperfect to the perfect. Hence, in speculative sciences, we see that the teaching of the early philosophers was imperfect, and that it was afterwards perfected by those who succeeded them. So also in practical matters: for those who first endeavored to discover something useful for the human community, not being able by themselves to take everything into consideration, set up certain institutions which were deficient in many ways; and these were changed by subsequent lawgivers who made institutions that might prove less frequently deficient in respect of the common weal.On the part of man, whose acts are regulated by law, the law can be rightly changed on account of the changed condition of man, to whom different things are expedient according to the difference of his condition. An example is proposed by Augustine (De Lib. Arb. i, 6): "If the people have a sense of moderation and responsibility, and are most careful guardians of the common weal, it is right to enact a law allowing such a people to choose their own magistrates for the government of the commonwealth. But if, as time goes on, the same people become so corrupt as to sell their votes, and entrust the government to scoundrels and criminals; then the right of appointing their public officials is rightly forfeit to such a people, and the choice devolves to a few good men."

Reply to Objection: 1.
The natural law is a participation of the eternal law, as stated above (Question [91], Article [2]), and therefore endures without change, owing to the unchangeableness and perfection of the Divine Reason, the Author of nature. But the reason of man is changeable and imperfect: wherefore his law is subject to change. Moreover the natural law contains certain universal precepts, which are everlasting: whereas human law contains certain particular precepts, according to various emergencies.
A measure should be as enduring as possible. But nothing can be absolutely unchangeable in things that are subject to change. And therefore human law cannot be altogether unchangeable.
In corporal things, right is predicated absolutely: and therefore, as far as itself is concerned, always remains right. But right is predicated of law with reference to the common weal, to which one and the same thing is not always adapted, as stated above: wherefore rectitude of this kind is subject to change.

Whether human law should always be changed, whenever something better occurs?


Objection: 1. It would seem that human law should be changed, whenever something better occurs. Because human laws are devised by human reason, like other arts. But in the other arts, the tenets of former times give place to others, if something better occurs. Therefore the same should apply to human laws.
Further, by taking note of the past we can provide for the future. Now unless human laws had been changed when it was found possible to improve them, considerable inconvenience would have ensued; because the laws of old were crude in many points. Therefore it seems that laws should be changed, whenever anything better occurs to be enacted.
Further, human laws are enacted about single acts of man. But we cannot acquire perfect knowledge in singular matters, except by experience, which "requires time," as stated in Ethic. ii. Therefore it seems that as time goes on it is possible for something better to occur for legislation.

On the contrary
It is stated in the Decretals (Dist. xii, 5): "It is absurd, and a detestable shame, that we should suffer those traditions to be changed which we have received from the fathers of old."
I answer that
As stated above (Article [1]), human law is rightly changed, in so far as such change is conducive to the common weal. But, to a certain extent, the mere change of law is of itself prejudicial to the common good: because custom avails much for the observance of laws, seeing that what is done contrary to general custom, even in slight matters, is looked upon as grave. Consequently, when a law is changed, the binding power of the law is diminished, in so far as custom is abolished. Wherefore human law should never be changed, unless, in some way or other, the common weal be compensated according to the extent of the harm done in this respect. Such compensation may arise either from some very great and every evident benefit conferred by the new enactment; or from the extreme urgency of the case, due to the fact that either the existing law is clearly unjust, or its observance extremely harmful. Wherefore the jurist says [*Pandect. Justin. lib. i, ff., tit. 4, De Constit. Princip.] that "in establishing new laws, there should be evidence of the benefit to be derived, before departing from a law which has long been considered just."

Reply to Objection: 1.
Rules of art derive their force from reason alone: and therefore whenever something better occurs, the rule followed hitherto should be changed. But "laws derive very great force from custom," as the Philosopher states (Polit. ii, 5): consequently they should not be quickly changed.
This argument proves that laws ought to be changed: not in view of any improvement, but for the sake of a great benefit or in a case of great urgency, as stated above. This answer applies also to the Third Objection.

Whether custom can obtain force of law?


Objection: 1. It would seem that custom cannot obtain force of law, nor abolish a law. Because human law is derived from the natural law and from the Divine law, as stated above (Question [93], Article [3]; Question [95], Article [2]). But human custom cannot change either the law of nature or the Divine law. Therefore neither can it change human law.
Further, many evils cannot make one good. But he who first acted against the law, did evil. Therefore by multiplying such acts, nothing good is the result. Now a law is something good; since it is a rule of human acts. Therefore law is not abolished by custom, so that the mere custom should obtain force of law.
Further, the framing of laws belongs to those public men whose business it is to govern the community; wherefore private individuals cannot make laws. But custom grows by the acts of private individuals. Therefore custom cannot obtain force of law, so as to abolish the law.

On the contrary
Augustine says (Ep ad Casulan. xxxvi): "The customs of God's people and the institutions of our ancestors are to be considered as laws. And those who throw contempt on the customs of the Church ought to be punished as those who disobey the law of God."
I answer that
All law proceeds from the reason and will of the lawgiver; the Divine and natural laws from the reasonable will of God; the human law from the will of man, regulated by reason. Now just as human reason and will, in practical matters, may be made manifest by speech, so may they be made known by deeds: since seemingly a man chooses as good that which he carries into execution. But it is evident that by human speech, law can be both changed and expounded, in so far as it manifests the interior movement and thought of human reason. Wherefore by actions also, especially if they be repeated, so as to make a custom, law can be changed and expounded; and also something can be established which obtains force of law, in so far as by repeated external actions, the inward movement of the will, and concepts of reason are most effectually declared; for when a thing is done again and again, it seems to proceed from a deliberate judgment of reason. Accordingly, custom has the force of a law, abolishes law, and is the interpreter of law.

Reply to Objection: 1.
The natural and Divine laws proceed from the Divine will, as stated above. Wherefore they cannot be changed by a custom proceeding from the will of man, but only by Divine authority. Hence it is that no custom can prevail over the Divine or natural laws: for Isidore says (Synon. ii, 16): "Let custom yield to authority: evil customs should be eradicated by law and reason."
As stated above (Question [96], Article [6]), human laws fail in some cases: wherefore it is possible sometimes to act beside the law; namely, in a case where the law fails; yet the act will not be evil. And when such cases are multiplied, by reason of some change in man, then custom shows that the law is no longer useful: just as it might be declared by the verbal promulgation of a law to the contrary. If, however, the same reason remains, for which the law was useful hitherto, then it is not the custom that prevails against the law, but the law that overcomes the custom: unless perhaps the sole reason for the law seeming useless, be that it is not "possible according to the custom of the country" [*Question [95], Article [3]], which has been stated to be one of the conditions of law. For it is not easy to set aside the custom of a whole people.
The people among whom a custom is introduced may be of two conditions. For if they are free, and able to make their own laws, the consent of the whole people expressed by a custom counts far more in favor of a particular observance, that does the authority of the sovereign, who has not the power to frame laws, except as representing the people. Wherefore although each individual cannot make laws, yet the whole people can. If however the people have not the free power to make their own laws, or to abolish a law made by a higher authority; nevertheless with such a people a prevailing custom obtains force of law, in so far as it is tolerated by those to whom it belongs to make laws for that people: because by the very fact that they tolerate it they seem to approve of that which is introduced by custom.

Whether the rulers of the people can dispense from human laws?


Objection: 1. It would seem that the rulers of the people cannot dispense from human laws. For the law is established for the "common weal," as Isidore says (Etym. v, 21). But the common good should not be set aside for the private convenience of an individual: because, as the Philosopher says (Ethic. i, 2), "the good of the nation is more godlike than the good of one man." Therefore it seems that a man should not be dispensed from acting in compliance with the general law.
Further, those who are placed over others are commanded as follows (Dt 1,17): "You shall hear the little as well as the great; neither shall you respect any man's person, because it is the judgment of God." But to allow one man to do that which is equally forbidden to all, seems to be respect of persons. Therefore the rulers of a community cannot grant such dispensations, since this is against a precept of the Divine law.
3. Further, human law, in order to be just, should accord with the natural and Divine laws: else it would not "foster religion," nor be "helpful to discipline," which is requisite to the nature of law, as laid down by Isidore (Etym. v, 3). But no man can dispense from the Divine and natural laws. Neither, therefore, can he dispense from the human law.

On the contrary
The Apostle says (1Co 9,17): "A dispensation is committed to me."
I answer that Dispensation, properly speaking, denotes a measuring out to individuals of some common goods: thus the head of a household is called a dispenser, because to each member of the household he distributes work and necessaries of life in due weight and measure. Accordingly in every community a man is said to dispense, from the very fact that he directs how some general precept is to be fulfilled by each individual. Now it happens at times that a precept, which is conducive to the common weal as a general rule, is not good for a particular individual, or in some particular case, either because it would hinder some greater good, or because it would be the occasion of some evil, as explained above (Question [96], Article [6]). But it would be dangerous to leave this to the discretion of each individual, except perhaps by reason of an evident and sudden emergency, as stated above (Question [96], Article [6]). Consequently he who is placed over a community is empowered to dispense in a human law that rests upon his authority, so that, when the law fails in its application to persons or circumstances, he may allow the precept of the law not to be observed. If however he grant this permission without any such reason, and of his mere will, he will be an unfaithful or an imprudent dispenser: unfaithful, if he has not the common good in view; imprudent, if he ignores the reasons for granting dispensations. Hence Our Lord says (Lc 12,42): "Who, thinkest thou, is the faithful and wise dispenser [Douay: steward], whom his lord setteth over his family?"

Reply to Objection: 1. When a person is dispensed from observing the general law, this should not be done to the prejudice of, but with the intention of benefiting, the common good.
It is not respect of persons if unequal measures are served out to those who are themselves unequal. Wherefore when the condition of any person requires that he should reasonably receive special treatment, it is not respect of persons if he be the object of special favor.
Natural law, so far as it contains general precepts, which never fail, does not allow of dispensations. In other precepts, however, which are as conclusions of the general precepts, man sometimes grants a dispensation: for instance, that a loan should not be paid back to the betrayer of his country, or something similar. But to the Divine law each man stands as a private person to the public law to which he is subject. Wherefore just as none can dispense from public human law, except the man from whom the law derives its authority, or his delegate; so, in the precepts of the Divine law, which are from God, none can dispense but God, or the man to whom He may give special power for that purpose.



In due sequence we must now consider the Old Law; and (1) The Law itself; (2) Its precepts. Under the first head there are six points of inquiry:

(1) Whether the Old Law was good?

(2) Whether it was from God?

(3) Whether it came from Him through the angels?

(4) Whether it was given to all?

(5) Whether it was binding on all?

(6) Whether it was given at a suitable time?

Whether the Old Law was good?


Objection: 1. It would seem that the Old Law was not good. For it is written (
Ez 20,25): "I gave them statutes that were not good, and judgments in which they shall not live." But a law is not said to be good except on account of the goodness of the precepts that it contains. Therefore the Old Law was not good.
2. Further, it belongs to the goodness of a law that it conduce to the common welfare, as Isidore says (Etym. v, 3). But the Old Law was not salutary; rather was it deadly and hurtful. For the Apostle says (Rm 7,8, seqq.): "Without the law sin was dead. And I lived some time without the law. But when the commandment came sin revived; and I died." Again he says (Rm 5,20): "Law entered in that sin might abound." Therefore the Old Law was not good.
3. Further, it belongs to the goodness of the law that it should be possible to obey it, both according to nature, and according to human custom. But such the Old Law was not: since Peter said (Ac 15,10): "Why tempt you (God) to put a yoke on the necks of the disciples, which neither our fathers nor we have been able to bear?" Therefore it seems that the Old Law was not good.

On the contrary The Apostle says (Rm 7,12): "Wherefore the law indeed is holy, and the commandment holy, and just, and good."
I answer that Without any doubt, the Old Law was good. For just as a doctrine is shown to be good by the fact that it accords with right reason, so is a law proved to be good if it accords with reason. Now the Old Law was in accordance with reason. Because it repressed concupiscence which is in conflict with reason, as evidenced by the commandment, "Thou shalt not covet thy neighbor's goods" (Ex 20,17). Moreover the same law forbade all kinds of sin; and these too are contrary to reason. Consequently it is evident that it was a good law. The Apostle argues in the same way (Rm 7): "I am delighted," says he (verse 22), "with the law of God, according to the inward man": and again (verse 16): "I consent to the law, that is good."But it must be noted that the good has various degrees, as Dionysius states (Div. Nom. iv): for there is a perfect good, and an imperfect good. In things ordained to an end, there is perfect goodness when a thing is such that it is sufficient in itself to conduce to the end: while there is imperfect goodness when a thing is of some assistance in attaining the end, but is not sufficient for the realization thereof. Thus a medicine is perfectly good, if it gives health to a man; but it is imperfect, if it helps to cure him, without being able to bring him back to health. Again it must be observed that the end of human law is different from the end of Divine law. For the end of human law is the temporal tranquillity of the state, which end law effects by directing external actions, as regards those evils which might disturb the peaceful condition of the state. On the other hand, the end of the Divine law is to bring man to that end which is everlasting happiness; which end is hindered by any sin, not only of external, but also of internal action. Consequently that which suffices for the perfection of human law, viz. the prohibition and punishment of sin, does not suffice for the perfection of the Divine law: but it is requisite that it should make man altogether fit to partake of everlasting happiness. Now this cannot be done save by the grace of the Holy Ghost, whereby "charity" which fulfilleth the law . . . "is spread abroad in our hearts" (Rm 5,5): since "the grace of God is life everlasting" (Rm 6,23). But the Old Law could not confer this grace, for this was reserved to Christ; because, as it is written (Jn 1,17), the law was given "by Moses, grace and truth came by Jesus Christ." Consequently the Old Law was good indeed, but imperfect, according to He 7,19: "The law brought nothing to perfection."

Reply to Objection: 1. The Lord refers there to the ceremonial precepts; which are said not to be good, because they did not confer grace unto the remission of sins, although by fulfilling these precepts man confessed himself a sinner. Hence it is said pointedly, "and judgments in which they shall not live"; i.e. whereby they are unable to obtain life; and so the text goes on: "And I polluted them," i.e. showed them to be polluted, "in their own gifts, when they offered all that opened the womb, for their offenses."
The law is said to have been deadly, as being not the cause, but the occasion of death, on account of its imperfection: in so far as it did not confer grace enabling man to fulfil what is prescribed, and to avoid what it forbade. Hence this occasion was not given to men, but taken by them. Wherefore the Apostle says (Rm 5,11): "Sin, taking occasion by the commandment, seduced me, and by it killed me." In the same sense when it is said that "the law entered in that sin might abound," the conjunction "that" must be taken as consecutive and not final: in so far as men, taking occasion from the law, sinned all the more, both because a sin became more grievous after law had forbidden it, and because concupiscence increased, since we desire a thing the more from its being forbidden.
3. The yoke of the law could not be borne without the help of grace, which the law did not confer: for it is written (Rm 9,16): "It is not him that willeth, nor of him that runneth," viz. that he wills and runs in the commandments of God, "but of God that showeth mercy." Wherefore it is written (Ps 118,32): "I have run the way of Thy commandments, when Thou didst enlarge my heart," i.e. by giving me grace and charity.

Whether the Old Law was from God?


Objection: 1. It would seem that the Old Law was not from God. For it is written (
Dt 32,4): "The works of God are perfect." But the Law was imperfect, as stated above (Article [1]). Therefore the Old Law was not from God.
2. Further, it is written (Qo 3,14): "I have learned that all the works which God hath made continue for ever." But the Old Law does not continue for ever: since the Apostle says (He 7,18): "There is indeed a setting aside of the former commandment, because of the weakness and unprofitableness thereof." Therefore the Old Law was not from God.
3. Further, a wise lawgiver should remove, not only evil, but also the occasions of evil. But the Old Law was an occasion of sin, as stated above (Article [1], ad 2). Therefore the giving of such a law does not pertain to God, to Whom "none is like among the lawgivers" (Jb 36,22).
4. Further, it is written (1Tm 2,4) that God "will have all men to be saved." But the Old Law did not suffice to save man, as stated above (Article [1]). Therefore the giving of such a law did not appertain to God. Therefore the Old Law was not from God.

On the contrary Our Lord said (Mt 15,6) while speaking to the Jews, to whom the Law was given: "You have made void the commandment of God for your tradition." And shortly before (verse 4) He had said: "Honor thy father and mother," which is contained expressly in the Old Law (Ex 20,12 Dt 5,16). Therefore the Old Law was from God.
I answer that The Old Law was given by the good God, Who is the Father of Our Lord Jesus Christ. For the Old Law ordained men to Christ in two ways. First by bearing witness to Christ; wherefore He Himself says (Lc 24,44): "All things must needs be fulfilled, which are written in the law . . . and in the prophets, and in the psalms, concerning Me": and (Jn 5,46): "If you did believe Moses, you would perhaps believe Me also; for he wrote of Me." Secondly, as a kind of disposition, since by withdrawing men from idolatrous worship, it enclosed [concludebat] them in the worship of one God, by Whom the human race was to be saved through Christ. Wherefore the Apostle says (Ga 3,23): "Before the faith came, we were kept under the law shut up [conclusi], unto that faith which was to be revealed." Now it is evident that the same thing it is, which gives a disposition to the end, and which brings to the end; and when I say "the same," I mean that it does so either by itself or through its subjects. For the devil would not make a law whereby men would be led to Christ, Who was to cast him out, according to Mt 12,26: "If Satan cast out Satan, his kingdom is divided" [Vulg.: 'he is divided against himself']. Therefore the Old Law was given by the same God, from Whom came salvation to man, through the grace of Christ.

Reply to Objection: 1. Nothing prevents a thing being not perfect simply, and yet perfect in respect of time: thus a boy is said to be perfect, not simply, but with regard to the condition of time. So, too, precepts that are given to children are perfect in comparison with the condition of those to whom they are given, although they are not perfect simply. Hence the Apostle says (Ga 3,24): "The law was our pedagogue in Christ."
2. Those works of God endure for ever which God so made that they would endure for ever; and these are His perfect works. But the Old Law was set aside when there came the perfection of grace; not as though it were evil, but as being weak and useless for this time; because, as the Apostle goes on to say, "the law brought nothing to perfection": hence he says (Ga 3,25): "After the faith is come, we are no longer under a pedagogue."
3. As stated above (Question [79], Article [4]), God sometimes permits certain ones to fall into sin, that they may thereby be humbled. So also did He wish to give such a law as men by their own forces could not fulfill, so that, while presuming on their own powers, they might find themselves to be sinners, and being humbled might have recourse to the help of grace.
Although the Old Law did not suffice to save man, yet another help from God besides the Law was available for man, viz. faith in the Mediator, by which the fathers of old were justified even as we were. Accordingly God did not fail man by giving him insufficient aids to salvation.

Summa Th. I-II EN Qu.96 a.5