Rashi on Numbers 16:3/רש"י על במדבר ט״ז:ג׳

1רב לכם You TAKE TOO MUCH UPON YOU — i.e. much more than is proper have you taken for yourselves in the way of high Office.

2כלם קדשים [FOR] ALL [THE CONGREGATION] ARE HOLY — they all heard the utterances on Sinai from the mouth of the Almighty (Midrash Tanchuma, Korach 4).

3ומדוע תתנשאו WHY THEN LIFT YE UP YOURSELVES [ABOVE THE ASSEMBLY OF THE LORD] — “If you have taken royal rank for yourself, you should at least not have chosen the priesthood for your brother — it is not you alone who have heard at Sinai: ‘I am the Lord thy God', all the congregation heard it!” (Midrash Tanchuma, Korach 4).