John Gill Commentary Deuteronomy 31:25

"that Moses commanded the Levites, that bare the ark of the covenant of Jehovah, saying," — Deuteronomy 31:25 (ASV)

That Moses commanded the Levites
These were not the common Levites, but the priests who were also Levites, to whom the law was given, (Deuteronomy 31:9) ; and none but they might touch the ark, or go so near it as, they are bid to do, to put the law on the side of it; so Aben Ezra; it follows,

which bare the ark of the covenant of the Lord ;
as the priests are said to do, (See Gill on Deuteronomy 31:9); for though in journeying the Kohathites carried it, yet not until it was covered by the priests, for they must not touch it; as these must do when they put the law on the side of it, as they are ordered in (Deuteronomy 31:26) .

saying ;
as follows.