What are the connotations of the words "Tifk'du osam"?
Ramban: It means 'Remember and take note of them!' 1 In other words, Moshe was not just commanded to count Yisrael but to know their numbers by accepting their half-Shekalim as an atonement, so that they should not be subject to a plague that ensues when Yisrael are counted S'tam. 2
Targum Onkelos and Targum Yonasan: It means simply, 'You shall count them!'
Ramban: It is a Lashon of 'Hashgachah' (supervision), and is similar to the Pasuk in Vayeira, Bereishis 21:1 "va'Hashem Pakad es Sarah'.
Ramban: Similar to David ha'Melech, about whom the Pasuk writes in Shmuel 2, 24:9, "Mispar Mifkad ha'Am". See Ramban, who takes for granted that David ha'Melech too, counted the people via half-Shekalim, and goes into detail to explain David's sin that caused the ensuing plague.
Why does Torah insert the words "Kol Yotzei Tzava" here?
Rashi: To teach us that a man under the age of twenty cannot be conscripted. 1
Ramban and Moshav Zekenim: It refers (not to the army, but) to being called to attend public gatherings, 2 from which the youth are generally precluded. 3
Oznayim la'Torah: The Torah is informing us of the miracle that al the men between the ages of twenty and sixty, who were being counted were strong and fit to be conscripted - that there was not a weak person or one with a blemish among them!
Ramban and Moshav Zekenim: Perhaps this is because it is only when a man turns twenty that he is strong enough to serve in the army, as the Mishnah states in Avos 'ben Esrim Lirdof'.
Ramban: Like we find later in Beha'aloscha, 8:24 & 25, and in Vayakhel, Sh'mos 38:8.
Ramban: And the Torah adds "le'Tziv'osam, because each tribe comprised large numbers.
Why is Aharon mentioned here, but not in the census at the beginning of Ki Sisa?
Ba'al ha'Turim: Because the census in Ki Sisa was instituted as a result of the Eigel, 1 for which Aharon was considered responsible, therefore it was inappropriate for him to have a hand in the counting.
To ascertain how many remained alive after the plague (Rashi on Pasuk 1).
Why were Yisrael counted from the age of twenty?
Refer to 1:3:2:1 and note.
Moshav Zekenim: A man of twenty has many Mitzvos ? from five he learns Mikra, from ten he learns Mishnah, from thirteen he is obligated to keep Mitzvos, from fifteen he learns Gemara. At twenty he has many Mitzvos which enable him to chase [the enemy] in war.
