John Calvin Commentary Deuteronomy 31:24

"And it came to pass, when Moses had made an end of writing the words of this law in a book, until they were finished," — Deuteronomy 31:24 (ASV)

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 contained in this book, but in the other three also. There is an implied antithesis between the two tablets written by God’s hand and the exposition that was afterward added, to prevent any obscurity concerning God’s will due to the brevity with which it was delivered. At the very beginning, indeed, God had set forth whatever it was useful for them to know. However, it was His will that what He had briefly included in the Decalogue should be more fully unfolded, and not only that, but it should also be committed to writing, so that it would not be forgotten.

We know how inclined the human mind is to vanity; indeed, how willfully it is led away into error by its fickleness, while it also has other faults, such as inquisitiveness, audacity in invention, and the love of novelty. Thus, religion would have been corrupted in a thousand ways if its rule had not 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 Tablets were enclosed in the Ark of the Covenant, a place at the side was assigned to the interpretation, so that they would have no doubt that it proceeded from the same Divine Author; and, since the Decalogue is repeated in these books, it was not at all necessary to open the Ark (which was not lawful), because they could seek in the books of Moses the instruction that was hidden in the Tablets.

Indeed, we must remember this: the volume was placed near the Ark as a sign of its dignity, so that, when it was taken from there by the Levites, it would 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 part of the whole body.

Furthermore, although the application of its doctrine is manifold, still only one point is referred to; for the Law was not written with the single object of being a witness to condemn the people, but also to be the rule of a pious and holy life and a testimony of God’s favor. But, since he was dealing with hard and proud minds, Moses declares that, whenever its doctrine is set forth, it will make their perverseness inexcusable.