John Gill Commentary Numbers 16:21

"Separate yourselves from among this congregation, that I may consume them in a moment." — Numbers 16:21 (ASV)

Separate yourselves, from among this congregation
Not only from Korah's company, but from the congregation of the children of Israel, whom Korah has got together, besides the two hundred fifty men that were at first with him; who by their words and behaviour, and particularly by their association and standing along with him, showed them to be on his side, which greatly provoked the Lord: that I may consume them in a moment ;
by fire from him, as the two hundred fifty men were afterwards consumed, (Numbers 16:35) .