Why did Hashem say "Heromu", and not "Hibadlu" as He did earlier in 16:21?
Rashbam: "Heromu" implies further away than "Hibadlu" - because here the plague had already begun to take effect.
Riva (16:21, citing R"M of Kutzi): Above, before the punishment, all the Machanos were together, and people needed to separate. After they were swallowed, people had already separated. Now they were told to distance further. 1
Maharil Diskin: It is an expression of taking Terumah. Hashem was angry, so He wanted to take a generous Shi'ur of Terumah, and kill one part in 40 of Yisrael, i.e. 15,088 and three quarters. 2 (One would not die due to the fraction; even one part in 1000 saves
He connotes that Moshe and Aharon told this to Am Yisrael. Who was the evil Edah from whom they must separate? Korach, Dasan and Aviram were swallowed, and the 250 were burned. Seemingly, Hashem told Moshe and Aharon to separate from Yisrael! (PF)
This is based on the census above (1:46). Why did Hashem take only based on the number of men above 20, and not from Levi? A Levi started this debacle! Also, many died in between, e.g. at Tav'eirah, Kivros ha'Ta'avah and the Meraglim! Perhaps just like the decree to die in the Midbar was only on Yisraelim counted, also this Terumah was only from them. Why does the calculation omit other family members of Korach, Dasan and Aviram? Do not say that it counts only Yisraelim counted, for it includes Korach! This requires investigation. (PF)
Why here, and above (16:21), did Hashem instruct the people to leave the vicinity of the sinners? He could simply have shielded them, like in Makas Bechoros, and throughout the ages, 'Three men sleep under one cover, and the two outer ones died, and the middle one survived!'
Ramban #1: Because Hashem's anger was vent against the people, to kill them all because they were beginning to join forces with the sinners. 1
Ramban #2: This was in honor of the Tzadikim, Moshe and Aharon, because as long as they were standing there, Hashem would not punish the sinners.
Ramban: Both earlier, by Dasan and Aviram and here. Indeed, in both cases, the ensuing plague was one that would automatically engulf whoever was to be found in its vicinity. Refer also to 16:21:2:2. (He did not answer that when Androlomusiya comes to the world, it kills Tzadikim and Resha'im, for that is only due to Zenus; refer to Bereishis 6:13:2:1.
Why did Moshe and Aharon fall on their faces but did not Daven, as Moshe did above in 16:22?