*Minor differences ignored. Grouped by changes, with first version listed as example.
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.
OF THE LEVITES' SERVICE. (Numbers. 4:1-49)
sons of Kohath, from thirty years old and upward--This age was specifically fixed (see on Numbers 8:24) as the full maturity of bodily energy to perform the laborious duties assigned them in the wilderness, as well as of mental activity to assist in the management of the sacred services. And it was the period of life at which John the Baptist and Christ entered on their respective ministries.
even unto fifty--The term prescribed for active duty was a period of twenty years, at the end of which they were exempted from the physical labors of the office, though still expected to attend in the tabernacle (Numbers 8:26).
all that enter into the host--so called from their number, the order and discipline maintained through their ranks, and their special duty as guards of the tabernacle. The Hebrew word, however, signifies also a station or office; and hence the passage may be rendered, "All that enter into the sacerdotal office" (Numbers 4:23).
Service of the Kohathites, and the number qualified for service. - Numbers 4:2, Numbers 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.
*More commentary available at chapter level.