Albert Barnes Commentary Deuteronomy 31:24-29

"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, that Moses commanded the Levites, that bare the ark of the covenant of Jehovah, saying, Take this book of the law, and put it by the side of the ark of the covenant of Jehovah your God, that it may be there for a witness against thee. For I know thy rebellion, and thy stiff neck: behold, while I am yet alive with you this day, ye have been rebellious against Jehovah; and how much more after my death? Assemble unto me all the elders of your tribes, and your officers, that I may speak these words in their ears, and call heaven and earth to witness against them. For I know that after my death ye will utterly corrupt yourselves, and turn aside from the way which I have commanded you; and evil will befall you in the latter days; because ye will do that which is evil in the sight of Jehovah, to provoke him to anger through the work of your hands." — Deuteronomy 31:24-29 (ASV)

Moses completes the writing of the Book of the Law, and directs that it be placed by the ark of the covenant.

The “book” referred to here would contain the whole Pentateuch up to this verse, and be “the Book of Moses,” called generally by the Jews “the Law” (Galatians 4:21) (Deuteronomy 31:24).

The Levites, who bore the ark—that is, as in Deuteronomy 31:9, “the priests the sons of Levi.” The non-priestly Levites could not even enter the sanctuary or touch the ark . Though in the journeys through the wilderness the ark was borne by the non-priestly Kohathites, yet on occasions of a more solemn and public character it was carried by the priests themselves (Joshua 3:3 and following; Joshua 4:9–10; Joshua 6:6, 12; Joshua 8:33; 1 Kings 8:3) (Deuteronomy 31:25).

Put it in the side of the ark—Rather, by the side of the ark. The two tablets of the Decalogue were in the ark (1 Kings 8:9); the Book of the Law was to be placed in the Holy of Holies near the ark of the covenant, probably in a chest (compare to 2 Kings 22:8) (Deuteronomy 31:26).

How much more after my death—Therefore, Deuteronomy 31:24 and the rest of the book (with the exception of the song, Deuteronomy 31:19) must be regarded as a kind of appendix added by another hand after Moses’ death; though the Blessing (Deuteronomy 33) is, of course, to be regarded as a composition of Moses (Deuteronomy 31:27).