These were counted from the Kohathite clans, everyone who could serve at the Tent of Meeting. Moses and Aaron numbered them according to the command of the LORD through Moses.
KJV
These [were] they that were numbered of the families of the Kohathites, all that might do service in the tabernacle of the congregation, which Moses and Aaron did number according to the commandment of the LORD by the hand of Moses.
ASV
These are they that were numbered of the families of the Kohathites, all that did serve in the tent of meeting, whom Moses and Aaron numbered according to the commandment of Jehovah by Moses.