Why did Hashem say "Heromu", and not 'Hibadlu' as He did earlier in 16:21?
Rashbam: "Heromu" implies further away than "Hibadlu" - because now the plague had already begun to take effect.
Riva (in 16:21, citing R"M of Kutzi): Before the punishment, all the camps were together, and the people needed to separate. After they were swallowed, people had already separated. Now they were told to distance themselves still 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 in forty of Yisrael - fifteen thousand and eighty-eight and three quarters. 2 (One would not die due to the fraction and even one part in thousand saves ? Shabbos 32a.) Three people (Korach, Dasan and Aviram) were swallowed, two hundred and fifty died through the Ketores, and fourteen thousand, seven hundred in the plague (17:14). Aharon ran among the Kahal and saved the lives of a hundred and thirty-five 3 men who should have died.
Oznayim la'Torah: Because,in the earlier Pasuk, Hashem was instructing Moshe and Aharon to separate from the congregation of Korach, Dasan and Aviram, where they were standing; whereas here, where they had already separated from them - See Pasuk 8 - He was instructing them to separate their minds from them, and not to Daven on their behalf. 4
He implies that Moshe and Aharon told this to the people. Who was the evil Eidah from whom they must separate? Korach, Dasan and Aviram were swallowed, and the two hundred nd fifty men were burned. Seemingly, Hashem told Moshe and Aharon to separate from Yisrael (PF). Refer to 17:10:2:1 & 2.
This is based on the census above (1:46). Why did Hashem take only based on the number of men above twenty and not from Levi? A Levi started this debacle! Also, many died in between - at Tav'eirah, Kivros ha'Ta'avah and the Meraglim! Perhaps just like the decree to die in the Midbar was only on Yisre'elim 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 Yisre'elim counted, for it includes Korach! This requires investigation (PF).
Maharil Diskin: The Gematriya of "Kahal". See Pasuk 12.
See Oznayim la'Torah, DH 'Heromu'.
Why here, and earlier in 16:21, did Hashem instruct the people to leave the vicinity of the sinners? Why did he not simply shield them, like He did in Makas B'choros, and throughout the ages ('Three men sleep under one cover, and the two outer ones die, and the middle one survives')?
Ramban #1: Because Hashem's anger was vented against the people, to kill them all because they were beginning to join forces with those who were grumbling (or who had come to kill Moshe and Aharon - Oznayim la'Torah). 1
Ramban #2: He was instruting Moshe and Aharon to separate from the people, whom He would not strike as long as they were standing in their vicinity.
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, since that is confined to the sin of immorality and idolatry. Refer to No'ach Bereishis, 6:13:2:1. ? PF).
Why did Moshe and Aharon fall on their faces?
Targum Yonasan: They actually fell on their faces in order to Daven.
Ba'al ha'Turim: They fell on their faces and did not Daven, as they did in 16:22, because (when they tried to Daven, their Tefilah did not come out fluently 1 - and they understood that it would not be accepted. 2
Oznayim la'Torah: Because Hashem instructed them not to Daven. 3
