פּירוש אויף במדבר 8:7

הזה עליהם מי חטאת SPRINKLE UPON THEM WATER OF PURIFYING — water in which the ashes of the Red Heifer are mingled; on account of those among them who might have become unclean through contact with dead persons.

והעבירו, the vocalisation ve-he-eviru means that it is a modified version of the future tense known as vav hahipuch, the letter ו reversing the tense. Had the vocalisation been veha-aviru it would have been an imperative mode, just as in Exodus 8,4 העתירו אל ה', “plead with the Lord!”

הזה עליהם מי חטאת והעבירו תער על כל בשרם, “sprinkle upon them water of purification, and let them pass a razor over their entire flesh.” Ibn Ezra points out that the shaving of their flesh had preceded their being sprinkled with the waters of purification. [He derives this from the switch by the Torah from the singular הזה, an instruction to Moses, whereas the word והעבירו is in the plural, referring to something the Levites had already done.]

והעבירו תער AND LET THEM SHAVE [ALL THEIR FLESH] — I have found in the work of R. Moses the Preacher the following: Because they were made propitiatory substitutes for the firstborn who had worshipped the idol (the Golden Calf), and it (idolatry) is called (Psalms 106:28) “offerings to the dead”, and the leper is also called dead (cf. Numbers 12:12), it (Scripture) requires them to shave their body like lepers.