This law of Deuteronomy. (Menochius)

Some think that he had written so far before he came to the assembly, as well as the Canticle; because God commanded him the same day to ascend the mount, chap. xxxii. 48. (Calmet)

But Moses did not speak the discourses recorded in this book, at one time. After he had, therefore, dismissed the people with his blessing, and with an assurance that God would be with their newly appointed leader, he committed to writing what he had delivered by God’s order, at different times, and gave a copy of the Pentateuch to the priests, who were to keep it carefully on the side of the ark, and explain it to the people, particularly every seventh year. The Jews understand this law to mean the whole Pentateuch. It may denote also, more particularly (Haydock) Deuteronomy, as far as this place, or the 27th, and three subsequent chapters of it. He gave two copies; one to be deposited beside the ark, and the other (ver. 26,) to be kept by the priests. In all contracts of consequence, this method is observed, one copy being laid carefully by, and the other left in the hands of those who may be concerned, Jeremias xxxii. 12. The Rabbins say that 13 copies were taken; one for each of the 12 tribes, and one to be placed on the side of the ark. But of this new assertion we must not expect to hear any proof.

Priests, whose duty it is to instruct the people, Malachias ii. 7. (Calmet)

Ancients, or magistrates, who must put the law in execution, and guide their decisions by it. (Haydock)

The mention of the ark in this place, is to insinuate that the book was to be deposited on one side of it, ver. 26. The priests might carry the ark, if they thought proper, (Menochius) as they did sometimes on the more solemn occasions; (Josue ii., and vi., and 1 Kings iv. 4,) though the duty belonged to the Levites, Numbers iii., and iv. The pagans placed their sacred books in their temples, under the care of the priests, who were obliged to transcribe them. (Calmet)