Numbers 4:2

“Take the sum of the sons of Kohath from among the sons of Levi, etc.] 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,…”

“Num 3:19, Num 3:27 Numbers 4:3”

“Service of the Kohathites, and the number qualified for service. - Num 4:2, Num 4:3. "Take the sum of the sons of Kohath from among the sons of Levi:" i.e., by raising them out of the sum total of the Levites, by numbering them first and specially, viz., the men from 30 to 50 years of age, "every one who comes to the service," i.e., who has to enter upon service "to do work at the tabernacle." צבא (Angl. 'host') signifies military service, and is used here with special reference to the service of the Levites as the militia sacra of Jehovah. Numbers 4:4”