Numbers 4:2

Take the sum of the sons of Kohath from among the sons of Levi,.... They were to begin with them first, and number them:

after their families, by the house of their fathers; as many as were of the age after mentioned; and the reason why they began with Kohath, and not Gershon, the eldest son, as in the former numbering, was; not as Aben Ezra suggests, because of Moses and Aaron, who sprung from him, for that, if it had any strength in it, would have held good before; but rather, as Chaskuni and others, because the Kohathites carried the ark and other holy things; though the true reason seems to be, because of the order observed in taking down the tabernacle, and removing the parts of it, and the things in it; and it was most proper and reasonable, when they were about to take it down, first to take out the ark, table, c. which was the business of the Kohathites to carry next to take down the curtains, coverings, and hangings for the tabernacle and court, and the doors thereof, which were the charge of the Merarites; wherefore, in this order the sum out of each of them fit for business were ordered to be numbered.