Bámidbár Rási

On the first day of the second month, in the second year following the exodus from the land of Egypt, יהוה spoke to Moses in the wilderness of Sinai, in the Tent of Meeting, saying:

וידבר… במדבר סיני … באחד לחדש וגו׳ AND [THE LORD] SPOKE [UNTO MOSES] IN THE DESERT OF SINAI … ON THE FIRST DAY OF THE [SECOND] MONTH … [TAKE YE THE SUM OF ALL THE CONGREGATION] etc. — Because they were dear to him, He counts them every now and then: when they went forth from Egypt He counted them (Exodus 12:37), when many of them fell in consequence of their having worshipped the golden calf He counted them to ascertain the number of those left (cf. Rashi Exodus 30:16); when he was about to make His Shechinah dwell amongst them (i. e. when He commanded them to make a Tabernacle), He again took their census; for on the first day of Nisan the Tabernacle was erected (Exodus 40:2) and shortly afterwards, on the first day of Iyar, He counted them.

Do not on any account enroll the tribe of Levi or take a census of them with the Israelites.

אך את מטה לוי לא תפקד ONLY THOU SHALT NOT NUMBER THE TRIBE OF LEVI — The legion of the King is worthy to be numbered by itself (cf. Midrash Tanchuma, Bamidbar 15). — Another explanation is: The Holy One, blessed be He, foresaw that a decree would once be made against all those that had been numbered from twenty years and upwards, viz., that they should die in the wilderness (Numbers 14:29). He therefore said: Let these (the Levites) not be included amongst those now counted, in which case they must die, because they are Mine, since they did not sin by worshipping the golden calf (cf. Numbers Rabbah 3:7; Bava Batra 121b).

I hereby take the Levites from among the Israelites in place of all the male first-born, the first issue of the womb among the Israelites: the Levites shall be Mine.

ואני הנה לקחתי AND I, BEHOLD I HAVE TAKEN [THE LEVITES FROM AMONG THE CHILDREN OF ISRAEL] — This means: And I — whence do “I” claim the right on them from among the children of Israel, that the Israelites should have to hire them (cf. Rashi on v. 8) for My service? It is through the firstborn — to whom I surely have a title — that I have a claim on them (the Levites) and so I take them in their (the firstborns’) stead. For originally the service (the priestly functions) was performed by the firstborn, but when they (the Israelites and among them their firstborn too) sinned by worshipping the golden calf they became disqualified, and the Levites who had not worshipped the idol were chosen in their stead (cf. Zevachim 112b).

The clans of the Kohathites were to camp along the south side of the Tabernacle.

משפחת בני קהת יוחנו … תימנה THE FAMILY OF THE SONS OF KOHATH SHALL ENCAMP … SOUTHWARD — and next to them was the division of Reuben who, too, were encamped in the South (cf. Numbers 2:10) — “Woe to the wicked, woe to his neighbour!” It was on this account (on account of the friendship caused by this proximity) that some of them (the Reubenites) — Dathan and Abiram and 250 men (who were also mostly Reubenites, cf. Rashi on Numbers 16:1) — were punished together with Korah and his congregation, (cf. Numbers 16:32 ff.), because they were dragged into the quarrel with them (cf. Midrash Tanchuma, Vayera 12).