John Calvin on Numbers 8:19

19. And I have given the Levites. He declares on what terms He desires to have them as His own, viz., that they may be directed by Aaron, and obey his commands; for by “a gift” is not to be understood such an act as that whereby a person resigns and cedes his own right to another; but, when He devotes them to the ministry of the sanctuary, He desires that they should have a leader and master. At the end of the verse, Moses teaches that this is done for the advantage and profit of the whole people: whence it follows, that there was no room for ill-will towards them, unless the people should perhaps be annoyed that God had taken measures for their welfare. A two-fold advantage is pointed out; first, because they were to be the intercessors or ministers of reconciliation, (for either sense would be appropriate;) secondly, because, whilst they would be the guardians of the sanctuary, they would prevent the Israelites from bringing destruction upon themselves, by their rash approach to it.