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.