פּירוש אויף במדבר 8:11

והניף אהרן את הלוים תנופה AND AARON SHALL MAKE A WAVING WITH THE LEVITES — just as the guilt offering of the leper (to whom the Levites are compared in some respect; cf. Rashi on v. 7) required waving whilst alive. — Three times is the command of waving the Levites mentioned in this section (vv. 11, 13, 15): the first refers to the sons of Kohath; therefore (because it is they who are referred to) Scripture adds with regard to them, “that they may execute the service of the Lord” — for it was upon them (the sons of Kohath) that the service of the most holy objects: the Ark, the table, etc., devolved. The second refers to the sons of Gershon, and therefore Scripture adds with regard to them, “a waving for the Lord”, for upon them devolved the service of the holy (though not the most holy) objects: the hangings and the catches which were visible in the Holy of Holies. The third refers to the sons of Merari.

והניף אהרן את הלוים מאת בני ישראל, “and Aaron is to wave the Levites (as an offering) from the Children of Israel;” Aaron was chosen to do this as he was the agent appointed for this by the nation.

Requires waving. A leper is termed “dead” as it says at the end of the Parshah “please, let her not be like the dead” (12:12) and the Levites were as an atonement for the firstborn who worshiped idols, which is termed “sacrifices of the dead.” Therefore, the Levites required “live waving” like the guilt-offering of a leper. Furthermore, the waving of the Levites would only be possible while they were alive.