1)
Having already warned them to separate from the congregation (in Pasuk 21), why did Hashem see fit to warn them again?
1.
Targum Yonasan: Before He warned Moshe and Aharon to leave the vicinity of all the people; now, having accepted Moshe's Tefilah, He was warning all the people to leave the vicinity of Korach and his congregation. 1
2.
Seforno: Hashem clarified that he ordered them to leave the vicinity only of Korach's congregation.
