Korach: Chapter 3
Holy, pure

Rabbi Shimon says that Moses asked Korah and the others to come before him in the morning because morning is the time of holiness, of Chesed, and therefore of the priests. Essentially Moses was saying to them that if they remained on the side of Judgment the morning would not tolerate them and they would not be found holy and worthy of the priesthood. The matter would be tested by the offering of the incense, and the man who God chooses must be holy and not pure: the priest is holy and the Levite is pure.