What are the connotations of "Rav lachem!" and "u'Madu'a Tisnas'u al K'hal Hashem?
Rashi: 'You have taken for yourselves more than your fair share of greatness; If you (Moshe) took for yourself the kingship, you should not have picked for your brother the Kehunah!'
Seforno: Refer to 16:3:2:2 ... 'and why did you therefore block the Bechoros from performing the Avodah, inasmuch as you first acted as Kohen Gadol during the Shiv'as Yemei ha'Milu'im and then appointed Aharon as Kohen Gadol permanently.
And what did Korach mean when he described the entire communal as 'holy'?
Rashi: He meant that all of Yisrael were on the same footing, since they were all at Har Sinai where they had all heard "Anochi Hashem Elokecha" from the Mouth of Hashem.
Ramban (on Pasuk 19): He meant that the Avodah should revert to all of Yisrael, as it was originally. 1