Charles Spurgeon Commentary Numbers 8:19-22

"And I have given the Levites as a gift to Aaron and to his sons from among the children of Israel, to do the service of the children of Israel in the tent of meeting, and to make atonement for the children of Israel; that there be no plague among the children of Israel, when the children of Israel come nigh unto the sanctuary. Thus did Moses, and Aaron, and all the congregation of the children of Israel, unto the Levites: according unto all that Jehovah commanded Moses touching the Levites, so did the children of Israel unto them. And the Levites purified themselves from sin, and they washed their clothes: and Aaron offered them for a wave-offering before Jehovah; and Aaron made atonement for them to cleanse them. 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 8:19-22 (ASV)

How instructive all this is to us! We are not to begin blunderingly to serve God while we are yet in our sins, – before we have been sprinkled with the blood, – before we have been washed in the water which flowed with the blood, – before we have felt that razor that takes away from us all our own pride and glory. No; but when all that is done, then there is to be no delay: After that went the Levites in to do their service.