John Calvin Commentary Numbers 8:6

"Take the Levites from among the children of Israel, and cleanse them." — Numbers 8:6 (ASV)

Take the Levites from among. To take them from among the children of Israel is equivalent to subtracting them from the number of the people, so that they might not be included in the general census and accounted to be one of the tribes. This separation, then, as he will more clearly express a little further on, devoted the Levites to God for the service of the sanctuary.

That under this pretext the Papal clergy should claim immunity for themselves, so that they may live as they like in exemption from the laws, is not only an unsound deduction but one full of impious mockery. For, since the ancient priesthood attained its end in Christ, the succession they allege robs Christ of His right, as if the full truth had not been manifested in Him. Besides, inasmuch as all their privileges depend only on the primacy of the Pope, if they would have them ratified, they must prove, first of all, that the Pope is appointed by God’s command to be the head of the whole Church, and therefore that he is the successor of Christ.

As to Aaron, since he was the minister of their installation, in this way he was set over the Levites to rule them at his discretion. Meanwhile, this ministry is thus entrusted to a man in such a manner as not to obstruct God’s gratuitous good pleasure.