John Gill Commentary Numbers 8:22

"And after that went the Levites in to do their service in the tent of meeting before Aaron, and before his sons: as Jehovah had commanded Moses concerning the Levites, so did they unto them." — Numbers 8:22 (ASV)

And after that went the Levites in into the court of the tabernacle, being at the door of it when the above rites and ceremonies of their consecration were performed: to do their service in the tabernacle of the congregation, before Aaron and his sons; in their presence, and by their order, as they should direct them: as the Lord had commanded Moses, so did they to them; Aaron and his sons did to the then present Levites according to the command of God by Moses; they exactly observed every punctilio of it, and complied with it; and this the sons of Aaron did continually to the sons of the Levites, as Aben Ezra remarks, in all succeeding ages; when the Levites were consecrated to their service, the same things were done to them that are here ordered.