Earlier, in 3:15, the Levi'im were counted from the age of one month. Why are they now being counted between the ages of thirty and fifty?
Rashi: Because one of the tasks of the Levi'im was the transportation of the dismantled sections of the Mishkan, which required strength, and a person attains his full strength at the age of thirty, and it is at the age of fifty that it begins to wane. 1
Rashi: A fact that Chazal actually learn from here. See Oznayim la'Torah, who explains why the age of conscription to the army is from twenty to sixty.
How can we reconcile this Pasuk with the Pasuk in Beha'aloscha, 8:24, which gives the starting age of a Ben Levi as twenty-five?
Rashi (Ibid.): At the age of twenty-five, they came to do apprenticeship, 1 and at thirty, they began performing the Avodah. 2
Refer to 8:24:2:1-3.
Why, in 1:3, does the Torah use the Lashon of "Yotzei Tzava" in connection with B'nei Yisrael going to the army and "Ba la'Tzava" in connection with the Levi'im?
Oznayim la'Torah #1: Because whereas the soldiers went out to the battlefield to fight, the Levi'im gathered to the Ohel Mo'ed to perform the Avodah.
Oznayim la'Torah #2: Because when the army goes to fight, they leave (with permission) the realm of a number of Mitzvos, 1 whereas the Levi'im who come to the Ohel Mo'ed to perform the Avodah, come closer to Hashem in that they have to be more careful regarding the Dinim of Tum'ah, and regarding the additionsl Mitzvos of Kehunah and Leviyah, respectively.
Oznayim la'Torah: See Eruvin, 17, regarding the four things that become permitted in wartime.
