John Calvin 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 to do their service. In these words, Moses signifies that, in the type, nothing was omitted concerning the ancient priesthood that pertains to the legitimate service of God, the main point of which is obedience, and from this the purity that flows from it. The Levites are said to have done their service before Aaron, because they humbly submitted themselves to the yoke and allowed themselves to be controlled by the will of the priest, since God had so enjoined.

But the progress of the history will soon show how prone man’s nature is to rebellion. From this it arises that the end does not always correspond with the beginning, but that sad and unhappy conclusions sometimes follow successful beginnings.