John Calvin on Numbers 1:47-54

47. But the Levites, after the tribe of their fathers We shall indeed hereafter see that they also were numbered, but Moses means that they were not included in the general census of the people, because God had chosen them to be His own property, and thus had severed them from the rest of the people. He writes, therefore, that they “were not numbered in the midst of the others,” Among them. — A. V. i.e., so as promiscuously to form a part of the multitude. Now, lest any one should object that Moses acted ambitiously in thus bestowing on his own tribe extraordinary distinction, he declares that he did not do this spontaneously, but that it was at God’s bidding that the Levites had a separate class assigned to them; for translators render this passage amiss, “And God said to Moses,” So the Vulgate, v. 48. as if he stated that the tribe of Levi was then first set apart when the sum of the people was taken, since it would have been absurd to omit a part, unless God’s will had been already declared. Moses, therefore, shews why he passed over his own tribe, via, because God had consecrated the Levites for the keeping and service of the tabernacle. Now, if it was not lawful for the tabernacle to be carried or set up by all persons indiscriminately, its sanctity was enforced by this symbol; for religion would not have been held in so much reverence, if it had been allowable for all without distinction to meddle with the sacred things. Meanwhile, the Israelites were reminded that all without, exception were unworthy to present themselves before God, when they were forbidden from access to the sanctuary; whereas the dignity which was conferred upon a single tribe was no ground for boasting, since it depended merely on the good pleasure of God. God, then, gave the Levites access to His tabernacle, not because they had deserved that honor by any virtue of their own, but in order to afford a testimony of His gratuitous favor. At the same time, under this image He represented the future priesthood of Christ, in order that believers might be assured that the Mediator, by whom others might have access to God, was to be of the human race; and therefore God declares by Isaiah that He would take the Levites under the kingdom of Christ from the general and dispersed body of the people. (Isaiah 66:21.) As to what relates to their office, let it be sought in its proper place.

Deuteronomy 10

Deuteronomy 10:8, 9

8. At that time the Lord separated the tribe of Levi, to bear the ark of the covenant of the Lord, to stand before the Lord to minister unto him, and to bless in his name, unto this day.

8. In tempore illo separavit Jehova tribum Levi: ut gestaret Arcam foederis Jehovae, ut staret coram Jehova ad ministrandum ei, et ad benediecudum in nomine ipsius usqae ad diem hanc.

9. Wherefore Levi hath no part nor inheritance with his brethren; the Lord is his inheritance, according as the Lord thy God promised him.

9. Idcirco non fuit ipsi Levi portio et haereditas cum fratribus suis: Jehova est haereditas ejus, quemadmodumdixit ei Jehova Deus tuus.