Summa Theologica, by St. Thomas Aquinas, [1947], at sacred-texts.com
We must now consider the precepts pertaining to the aforesaid, and under this head there are two points of inquiry:
(1) The precepts concerning faith;
(2) The precepts concerning the gifts of knowledge and understanding.
Objection 1: It would seem that, in the Old Law, there should have been given precepts of faith. Because a precept is about something due and necessary. Now it is most necessary for man that he should believe, according to Heb. 11:6, "Without faith it is impossible to please God." Therefore there was very great need for precepts of faith to be given.
Objection 2: Further, the New Testament is contained in the Old, as the reality in the figure, as stated above (FS, Q[107], A[3]). Now the New Testament contains explicit precepts of faith, for instance Jn. 14:1: "You believe in God; believe also in Me." Therefore it seems that some precepts of faith ought to have been given in the Old Law also.
Objection 3: Further, to prescribe the act of a virtue comes to the same as to forbid the opposite vices. Now the Old Law contained many precepts forbidding unbelief: thus (Ex. 20:3): "Thou shalt not have strange gods before Me," and (Dt. 13:1-3) they were forbidden to hear the words of the prophet or dreamer who might wish to turn them away from their faith in God. Therefore precepts of faith should have been given in the Old Law also.
Objection 4: Further, confession is an act of faith, as stated above (Q[3], A[1]). Now the Old Law contained precepts about the confession and the promulgation of faith: for they were commanded (Ex. 12:27) that, when their children should ask them, they should tell them the meaning of the paschal observance, and (Dt. 13:9) they were commanded to slay anyone who disseminated doctrine contrary to faith. Therefore the Old Law should have contained precepts of faith.
Objection 5: Further, all the books of the Old Testament are contained in the Old Law; wherefore Our Lord said (Jn. 15:25) that it was written in the Law: "They have hated Me without cause," although this is found written in Ps. 34 and 68. Now it is written (Ecclus. 2:8): "Ye that fear the Lord, believe Him." Therefore the Old Law should have contained precepts of faith.
On the contrary, The Apostle (Rom. 3:27) calls the Old Law the "law of works" which he contrasts with the "law of faith." Therefore the Old Law ought not to have contained precepts of faith.
I answer that, A master does not impose laws on others than his subjects; wherefore the precepts of a law presuppose that everyone who receives the law is subject to the giver of the law. Now the primary subjection of man to God is by faith, according to Heb. 11:6: "He that cometh to God, must believe that He is." Hence faith is presupposed to the precepts of the Law: for which reason (Ex. 20:2) that which is of faith, is set down before the legal precepts, in the words, "I am the Lord thy God, Who brought thee out of the land of Egypt," and, likewise (Dt. 6:4), the words, "Hear, O Israel, the Lord thy [Vulg.: 'our'] God is one," precede the recording of the precepts.
Since, however, faith contains many things subordinate to the faith whereby we believe that God is, which is the first and chief of all articles of faith, as stated above (Q[1], AA[1],7), it follows that, if we presuppose faith in God, whereby man's mind is subjected to Him, it is possible for precepts to be given about other articles of faith. Thus Augustine expounding the words: "This is My commandment" (Jn. 15:12) says (Tract. lxxxiii in Joan.) that we have received many precepts of faith. In the Old Law, however, the secret things of faith were not to be set before the people, wherefore, presupposing their faith in one God, no other precepts of faith were given in the Old Law.
Reply to Objection 1: Faith is necessary as being the principle of spiritual life, wherefore it is presupposed before the receiving of the Law.
Reply to Objection 2: Even then Our Lord both presupposed something of faith, namely belief in one God, when He said: "You believe in God," and commanded something, namely, belief in the Incarnation whereby one Person is God and man. This explanation of faith belongs to the faith of the New Testament, wherefore He added: "Believe also in Me."
Reply to Objection 3: The prohibitive precepts regard sins, which corrupt virtue. Now virtue is corrupted by any particular defect, as stated above (FS, Q[18], A[4], ad 3; FS, Q[19], A[6], ad 1, A[7], ad 3). Therefore faith in one God being presupposed, prohibitive precepts had to be given in the Old Law, so that men might be warned off those particular defects whereby their faith might be corrupted.
Reply to Objection 4: Confession of faith and the teaching thereof also presuppose man's submission to God by faith: so that the Old Law could contain precepts relating to the confession and teaching of faith, rather than to faith itself.
Reply to Objection 5: In this passage again that faith is presupposed whereby we believe that God is; hence it begins, "Ye that fear the Lord," which is not possible without faith. The words which follow---"believe Him"---must be referred to certain special articles of faith, chiefly to those things which God promises to them that obey Him, wherefore the passage concludes---"and your reward shall not be made void."
Objection 1: It would seem that the precepts referring to knowledge and understanding were unfittingly set down in the Old Law. For knowledge and understanding pertain to cognition. Now cognition precedes and directs action. Therefore the precepts referring to knowledge and understanding should precede the precepts of the Law referring to action. Since, then, the first precepts of the Law are those of the decalogue, it seems that precepts of knowledge and understanding should have been given a place among the precepts of the decalogue.
Objection 2: Further, learning precedes teaching, for a man must learn from another before he teaches another. Now the Old Law contains precepts about teaching---both affirmative precepts as, for example, (Dt. 4:9), "Thou shalt teach them to thy sons"---and prohibitive precepts, as, for instance, (Dt. 4:2), "You shall not add to the word that I speak to you, neither shall you take away from it." Therefore it seems that man ought to have been given also some precepts directing him to learn.
Objection 3: Further, knowledge and understanding seem more necessary to a priest than to a king, wherefore it is written (Malachi 2:7): "The lips of the priest shall keep knowledge, and they shall seek the law at his mouth," and (Osee 4:6): "Because thou hast rejected knowledge, I will reject thee, that thou shalt not do the office of priesthood to Me." Now the king is commanded to learn knowledge of the Law (Deut. 17:18, 19). Much more therefore should the Law have commanded the priests to learn the Law.
Objection 4: Further, it is not possible while asleep to meditate on things pertaining to knowledge and understanding: moreover it is hindered by extraneous occupations. Therefore it is unfittingly commanded (Dt. 6:7): "Thou shalt meditate upon them sitting in thy house, and walking on thy journey, sleeping and rising." Therefore the precepts relating to knowledge and understanding are unfittingly set down in the Law.
On the contrary, It is written (Dt. 4:6): "That, hearing all these precepts, they may say, Behold a wise and understanding people."
I answer that, Three things may be considered in relation to knowledge and understanding: first, the reception thereof; secondly, the use; and thirdly, their preservation. Now the reception of knowledge or understanding, is by means of teaching and learning, and both are prescribed in the Law. For it is written (Dt. 6:6): "These words which I command thee . . . shall be in thy heart." This refers to learning, since it is the duty of a disciple to apply his mind to what is said, while the words that follow---"and thou shalt tell them to thy children"---refer to teaching.
The use of knowledge and understanding is the meditation on those things which one knows or understands. In reference to this, the text goes on: "thou shalt meditate upon them sitting in thy house," etc.
Their preservation is effected by the memory, and, as regards this, the text continues---"and thou shalt bind them as a sign on thy hand, and they shall be and shall move between thy eyes. And thou shalt write them in the entry, and on the doors of thy house." Thus the continual remembrance of God's commandments is signified, since it is impossible for us to forget those things which are continually attracting the notice of our senses, whether by touch, as those things we hold in our hands, or by sight, as those things which are ever before our eyes, or to which we are continually returning, for instance, to the house door. Moreover it is clearly stated (Dt. 4:9): "Forget not the words that thy eyes have seen and let them not go out of thy heart all the days of thy life."
We read of these things also being commanded more notably in the New Testament, both in the teaching of the Gospel and in that of the apostles.
Reply to Objection 1: According to Dt. 4:6, "this is your wisdom and understanding in the sight of the nations." By this we are given to understand that the wisdom and understanding of those who believe in God consist in the precepts of the Law. Wherefore the precepts of the Law had to be given first, and afterwards men had to be led to know and understand them, and so it was not fitting that the aforesaid precepts should be placed among the precepts of the decalogue which take the first place.
Reply to Objection 2: There are also in the Law precepts relating to learning, as stated above. Nevertheless teaching was commanded more expressly than learning, because it concerned the learned, who were not under any other authority, but were immediately under the law, and to them the precepts of the Law were given. On the other hand learning concerned the people of lower degree, and these the precepts of the Law have to reach through the learned.
Reply to Objection 3: Knowledge of the Law is so closely bound up with the priestly office that being charged with the office implies being charged to know the Law: hence there was no need for special precepts to be given about the training of the priests. On the other hand, the doctrine of God's law is not so bound up with the kingly office, because a king is placed over his people in temporal matters: hence it is especially commanded that the king should be instructed by the priests about things pertaining to the law of God.
Reply to Objection 4: That precept of the Law does not mean that man should meditate on God's law of sleeping, but during sleep, i.e. that he should meditate on the law of God when he is preparing to sleep, because this leads to his having better phantasms while asleep, in so far as our movements pass from the state of vigil to the state of sleep, as the Philosopher explains (Ethic. i, 13). In like manner we are commanded to meditate on the Law in every action of ours, not that we are bound to be always actually thinking about the Law, but that we should regulate all our actions according to it.