John Calvin Commentary Numbers 18:2

"And thy brethren also, the tribe of Levi, the tribe of thy father, bring thou near with thee, that they may be joined unto thee, and minister unto thee: but thou and thy sons with thee shall be before the tent of the testimony." — Numbers 18:2 (ASV)

And thy brethren also. Here he assigns their duties to the Levites, so that they also may minister, but, as it were, under the authority of the priests; namely, that they should be governed by their commands. Thus, the authority was in the hands of the priests, but the Levites assisted them.

For this reason, they are prohibited from approaching the altar or entering the greater sanctuary; in fact, a lower rank is assigned to them, halfway between the priests and the people.

From this, all learned how reverently God’s majesty must be served. For although God had adopted the whole people, it was so far from being lawful for any of the multitude to approach the altar, that the Law even kept the Levites back from there, despite their being God’s special ministers.

Moreover, in this figure, we perceive how necessary is a Mediator for us to reconcile us to God. For if it was not permitted for the holy and chosen seed of Abraham to approach the typical sanctuary, how could we, who were aliens,²⁰⁰ now enter heaven, unless a way of access were opened to us through Christ?

Finally, when He forbids strangers from interfering with holy things, He does not mean only foreigners, but all the people, except the tribe of Levi. For here a distinction is drawn, not between the Church and pagan nations, but between the ministers of the sanctuary and the rest of the people.

²⁰⁰ “Qui estions estrangers, et rejettez au pris d’eux.” —.” — Fr.