John Calvin Commentary Numbers 16:5

"and he spake unto Korah and unto all his company, saying, In the morning Jehovah will show who are his, and who is holy, and will cause him to come near unto him: even him whom he shall choose will he cause to come near unto him." — Numbers 16:5 (ASV)

And he spoke to Korah. Moses did not inconsiderately choose this mode of divination, but by the dictation of the Spirit maintained the priesthood of his brother by this sign and testimony. For we know how, in matters of doubt and obscurity, he was accustomed to inquire what God’s pleasure was. He did not, therefore, at this time make this proposal hastily and at random, but by the inspiration of the Spirit had recourse to the sure judgment of God. The effect of his prayer was that God suggested an easy and expeditious means of prevailing.

He instructs them to take their censers, so that by their incense-offering it might be manifested whether their offering was acceptable to God. By deferring it until the next day, he considered their own safety, if any of them might still not be incurable; for he saw that they were carried away headlong by blind fury and that they could not be recalled to their senses in a moment. He, therefore, grants them some time for repentance, so that they might be led to consideration during the night; or perhaps his purpose was that, with the tumult appeased, he might render them all attentive to the decision of God.