Deuteronomy 31:9

And Moses wrote this law
The book of Deuteronomy, or the Pentateuch, the five books of Moses, which he had now finished, and which all of them together are sometimes called the law, ( Galatians 4:21 ) ;

and delivered it unto the priests, the sons of Levi;
who were the teachers of the law, as Aben Ezra observes; see ( Malachi 2:7 ) ; and therefore it was proper to put it into their hands, to instruct the people in it, and that the people might apply to them in any matter of difficulty, or when they wanted to have any particular law explained to them:

which bare the ark of the covenant of the Lord;
for though they were the Levites, and particularly the Kohathites, who in journeying carried the ark; see ( Numbers 4:5-15 ) ( 10:21 ) ; yet sometimes it was borne by the priests; see ( Joshua 3:13-17 ) ( 6:6 ) ( 1 Samuel 4:4 ) ;

and unto all the elders of Israel;
the judges and civil magistrates in the respective tribes; for as there were in the book of the law several things which belonged to the priests to perform, and all of them they were to instruct in, so there were others which were to be the rule of judgment to judges, and all civil magistrates, and which they were to take care were put in execution; and therefore it was proper that they should have a copy of this law, and which must be here understood; for it cannot be thought that one and the same copy should be given both to the priests and to all the elders. The Jews say Moses wrote thirteen copies of the law, twelve for the twelve tribes, and one to be put into the ark, to convict of fraud or corruption, should any be made ^F19.