This was the list of the clans of the sons of Gershon, all who served in the tent of meeting, whom Moses and Aaron listed according to the commandment of the LORD.
We have here a particular account of the numbers of the three families of the Levites respectively, that is, of the effective men, between thirty years old and fifty. Observe, 1. The Kohathites were, in all, 8600 from a month old and upwards; but of these there were but 2750 serviceable men, not a third part.
Commenting on Numbers 4:34-49
These [are] they that were numbered of the families of the sons of Gershon, of all that might do service in the tabernacle of the congregation, whom Moses and Aaron did number according to the commandment of the LORD. (t) Which were of eligible age to serve in it, that is between 30 and 50.
Num 4:34-48 Completion of the prescribed mustering, and statement of the number of men qualified for service in the three Levitical families: viz., 2750 Kohathites, 2630 Gershonites, and 3200 Merarites - in all, 8580 Levites fit for service: a number which bears a just proportion to the total number of male Levites of a month old and upwards, viz., 22,000.
Commenting on Numbers 4:34-48