Charles Ellicott Commentary Numbers 4:15

"And when Aaron and his sons have made an end of covering the sanctuary, and all the furniture of the sanctuary, as the camp is set forward; after that, the sons of Kohath shall come to bear it: but they shall not touch the sanctuary, lest they die. These things are the burden of the sons of Kohath in the tent of meeting." — Numbers 4:15 (ASV)

And all the vessels of the sanctuary. —No mention is made here of the laver (Exodus 30:18). The Septuagint and the Samaritan text supply a statement regarding the covering and transport of the brazen laver. The clause in the Septuagint is as follows: And they shall take a purple cloth, and cover the laver and its foot (or base), and they shall put it into a blue cover of skin, and put it on bars. There is no sufficient ground, however, to suppose that the present Hebrew text is deficient here, and it seems more probable that the laver was not to be covered during its transport.

After that, the sons of Kohath shall come to bear it. —Better, to bear, or carry —namely, all the vessels of ministry that had been previously enumerated. The distinction between the service of the priests and that of the Levites regarding the removal of the Tabernacle and its furniture is clearly marked here.

But they shall not touch any holy thing, lest they die. —The word that is rendered “any holy thing” may, here as elsewhere, denote the sanctuary. This injunction is repeated in Numbers 18:3. We find in 2 Samuel 6:6–7 an instance of the fatal result of violating this command by Uzzah, who was most probably a Levite and of the family of Kohath, and ought to have been acquainted with the law regarding the removal of the Ark. It is obvious that the Kohathites, as the immediate assistants of the priests regarding the vessels of the Sanctuary, were specially exposed to the risk of violating the law by touching the most holy things.