Why did Hashem come down alone (in an Amud Anan) and not with an entourage?
Rashi: When Hakadosh-Baruch-Hu goes to war, He goes alone, 1 and when He goes for peace, He travels with His retinue. 2
Rashi: As the Torah writes in the Shirah "Hashem Ish Milchamah" - and His harsh rebuke of Miriam and Aharon was akin to an act of war
As the Pasuk writes in Tehilim, 68:18 - in connection with Matan Torah - "Rechev Ribosayim Alfei Shin'an".
Why did Hashem call Aharon and Miriam? Why did He now separate them from Moshe?
Rashi: So that they leave the Azarah where they had gathered together with Moshe - in order to relate the full praise of Moshe, and one relates only part of a Tzadik's praise in his presence. 1
Rashi #2: So that Moshe should not overhear when Hashem rebuked Aharon. 2
Rashi: Like we find by No'ach, whom Hashem referred to "Tzadik" in his presence (See Bereishis 7:1) and as "Tzadik Tamim" not in not in his presence.
Perhaps He was concerned only that he may he may overhear when He rebukes Aharon, for in any case he will know that Miriam was punished for a misdeed. (PF)
