Sforno on Numbers 16:7/ספורנו על במדבר ט״ז:ז׳

1הוא הקדוש, only he is the one accorded the title “holy.” In the test Moses proposes there could be only one winner. Moses made this statement in order to frighten his listeners (as they would become aware of the enormity of the gamble they were going to involve themselves in) and knowing this they might repent and not lose their lives. Just as G’d does not want the sinner to die but to repent, so Moses offered these people the chance to retract and thereby save their lives. (compare Ezekiel 18,32).

2רב לכם בני לוי, you, inasmuch as you are considered people belonging to Korach (compare verse 32), are being judged more sternly, exactingly, precisely because due to your superior social position you must lead even more exemplary lives than ordinary Israelites. G’d will be much more angry at you if you fail to reflect the nobility you already represent.