Numbers 18:2

2.And thy brethren also. He here assigns their duties to the Levites, that they also may minister, but, as it were, under the hand of the priests, viz., that they may be ruled by their commands. Thus the authority was in the hands of the priests, but the Levites afforded them their assistance. On this ground they are prohibited from approaching the altar, or entering the greater sanctuary; in fact, a lower degree is assigned to them, half-way between the priests and the people. Hence did all learn how reverently God’s majesty must be served; for although He had adopted the whole people, yet so far was it from being lawful that any of the multitude should penetrate to the altar, that the Law even kept back the Levites from thence, although they were God’s peculiar ministers. Moreover, in this figure, we perceive how necessary is a Mediator for us to conciliate God’s favor towards us; for, if it was not allowable for the holy and chosen seed of Abraham to approach the typical sanctuary, how should we, who were aliens, (200) now penetrate to heaven, unless a way of access were opened to us through Christ? Finally, when He forbids strangers from meddling 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 heathen nations, but between the ministers of the sanctuary and the rest of the people.