Or HaChaim on Numbers 16:16/אור החיים על במדבר ט״ז:ט״ז

1 אתה וכל עדתך היו לפני השם, "you and your whole congregation be in the presence of the Lord!" Why did Moses not include Aaron in the same breath, seeing he too was supposed to bring incense? Why did he mention Aaron separately? Had Moses done so he would not have had to repeat the words: "you and they." Perhaps Moses wanted to emphasise that the decision would be made on the morrow. He did not want to give the rebels a chance to put off the date of the confrontation and perhaps add to their numbers in the interval. As far as Aaron was concerned Moses did not worry about when the confrontation would take place. He only had to mention that Aaron too would bring his censer.

2Another reason Moses gave the people until the morning was so that they could sanctify themselves in the interval. This was the meaning of: "be in the presence of the Lord." He certainly did not have to include Aaron as amongst the people who had to sanctify themselves as Aaron was always in a state of readiness to present himself before G'd. He did have to tell Aaron to be present at that time on the morrrow. The reason the whole instruction has been repeated seeing Moses had already told Korach and associates to take censers for incense in verse 6, is that in the interval Moses had rebuked the rebels and pointed out to them that they were guilty of overreaching themselves. In view of the fact that these people did not accept Moses' rebuke he had to tell them again to prepare for the confrontation which would be the test.