Deuteronomy 31:24

24.And it came to pass, when Moses had made an end. By “the words of this law,” we must understand not only those which are embraced in this book, but in the other three also; and there is an implied antithesis between the two tables written by God’s hand, and the exposition which was afterwards added, lest there should be any obscurity respecting God’s will on account of the brevity with which it was delivered. At the very beginning, indeed, God had set forth whatever it was useful for them to know, but it was His will that what He had briefly comprehended in the Decalogue should be more fully unfolded, and not only so, but that it should be also committed to writing, lest it should be forgotten. We know how inclined to vanity is the mind of man, nay, how willfully it is led away into error by its levity; whilst it has other faults also, such as inquisitiveness, and audacity in invention, and the love of novelty. Thus religion would have been corrupted in a thousand ways, had not its rule been diligently written down for posterity. Moreover, since the books of Moses were for a long time buried through the carelessness of the people and the priests, what darkness of error would have overspread the minds of all, if nothing had been written down!

Since the two Tables were enclosed in the Ark of the Covenant, a place at the side was assigned to the interpretation, so that they might have no doubt but that it proceeded from the same Divine Author; and, since the Decalogue is repeated in these books, it was not at all necessary that the Ark should be opened; which was not lawful, because they might seek in the books of Moses the instruction which was hidden in the Tables. This, indeed, we must remember, that the volume was placed near the Ark in token of its dignity, so that, when it was taken from thence by the Levites, it might be listened to with greater reverence. When it is said, “That it may be there for a witness against thee,” this is not addressed to the Levites alone, but relates generally to the whole people, though the general statement is directed to them as one member of the whole body. But further, although the application of its doctrine is manifold, still one point only is adverted to; for the Law was not written with the single object of being a witness to condemn the people, but to be the rule of a pious and holy life, and a testimony of God’s favor. But, since he had to do with hard and proud minds, Moses declares that, whenever its doctrine shall be set forth, it will render their perverseness inexcusable.