What is the significance of this punishment?
Rashi: Refer 1 to 32:20:1:1*.
Ramban: Refer to 32:27:5:3 & 4.
Targum Yonasan: Refer to 32:20:1:3.
See Sifsei Chachamim here.
Why did the plague occur here, after Hashem had already punished the chief sinners and instructed Moshe to lead the people to Eretz Yisrael?
Ramban #1: It was an additional layer of atonement to render them worthy of achieving that end.
Ramban #2: Because the decree had been issued already before but took effect only now.
Targum Yonasan: This punishmentt was meted out to those who prostrated themselves before the Eigel.
Why does the Torah not inform us how many people died in the plague (as it did by Korach, in Bamidbar 17:14, and by Ba'al Pe'or, in Bamidbar, 25:9?
Ramban #1 and Moshav Zekenim #1: Becsuse the plague was not one that took immediate effect; It took the form of a decree that they would all die prematurely. 1
Ramban #2 and Moshav Zekenim #2: Because the Torah does not always make a point of informing us as to the number of people who died. 2
As we find in Shmuel 1, 26:10 (Ramban).
Ramban and Moshav Zekenim: See for example, Bamidbar 11:1, and Bamidbar 11:33. The Torah does however, present the number of people killed by the B'nei Levi, in praise of the Levi'im, who placed their faith in Hashem and were not afraid of the victims overpowering them.
Why does the Torah insert the (otherwise superfluous) phrase "Al asher Asu es ha'Eigel Asher Asah Aharon"?
Ramban and Moshav Zekenim: Because the plague did not kill those who bowed down to the Eigel or those who sacrificed to it, only those who congregated on Aharon and brought gold to him - and upon whose instructions Aharon made it.
