Why does the Tirah switch from the Lashon "le'Mishpechosan le'Veis Avosam", which it uses by the other tribes, to "le'Veis Avosam
le'Mishpechosan "?
1.
Oznayim la'Torah: Because "Beis Avosam" by the Levi'im refers to Gershon, K'has and Merari - which is the equivalent of the tribe by all the others - and is not sunonymous with "Beis Avosam" by al the other tribes - in which takes it obviously comes before "Mishpechosam".
2)
Why were the Levi'im counted only from the age of thirty days and not from birth?
1.
Rashi: Because the first thirty days after a person is born he is a Safek Nefel (miscarriage). From the moment that he leaves that Safek, however, he falls under the category of 'Shomer Mishmeres ha'Kodesh".
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2.
Rashbam: Because since they were coming to redeem the firstborn, who could only be redeemed after thirty days,
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they too, were counted from thirty days (even though they were not yet fit to perform the Avodah - Oznayim la'Torah).
Rashi (citing R. Yehudah b'R. Shalom): The tribe of Levi was already accustomed to being counted from birth, as the Pasuk states in Pinchas, 26:59 (regarding the birth of Yocheved) "asher Yaldah osah le'Levi be'Mizrayim" (Levi's wife bore her to Levi in Egypt) - as they entered Egypt. And she completed the count of the 'seventy souls who came down to Egypt' (See Rashi).
Why does the Torah not mention Aharon here, like it does later in 3:59?
1.
Ramban: Hashem instructed Moshe alone to count them, and it was Moshe, of his own accord, who asked Aharon to join him, since he was the Nasi of Shevet Levi.
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