Numbers 16:12

Moshe sent, etc. From here [we derive] that one should not maintain a dispute, for Moshe sought them out in order to come to terms with them through a peaceful dialogue.

We will not go up. Their own words caused them to stumble — they will have nothing but a downfall.

And Mosheh sent men to summon Dathan and Abiram, the sons of Eliab, to the house of the great judgment; but they said, We will not come up.

We will not go up. It is possible that the Tent of Meeting was located on high ground within the camp, and therefore it was appropriate to use the language “go up.” Alternatively, it can be explained that one who goes to the service of Hashem or to the chosen place is going up.

AND MOSES SENT TO CALL DATHAN AND ABIRAM. Now Dathan and Abiram were the instigators of this controversy as much as Korach was, as Scripture states, Now Korach took … and Dathan and Abiram … and they rose up in the face of Moses with certain of the children of Israel etc., meaning that they were the ones who roused them together against Moses and Aaron. Then Moses spoke [once] to Korach and to all his company, and furthermore said to him: thou and all thy company, for it was to him [Korach] that he spoke first, since he was the leader amongst them. Now amongst those that were gathered together were also the followers of Dathan and Abiram; therefore Moses wanted to speak to them also now, and to warn them about themselves and all those who were gathered together [with them], who were their company, and to appease them with good words, even comforting words to Israel, since his [earlier] words to Korach were a conciliation only to the Levites.
The meaning of the expression and Moses sent is that Dathan and Abiram had gone away from his presence whilst he was speaking to Korach [as stated in Verses 5-7], and afterwards it again says, And Moses said unto Korach [Verse 8], who was still standing before him there, or maybe since Korach was a Levite he stayed in the camp of the Levites near the tent of Moses. All this happened on the first day [of the rebellion], just as Moses said, thou and they, and Aaron tomorrow, — this being the “morning” he mentioned to them: In the ‘morning’ the Eternal will make it known who are His.
It is possible that Dathan and Abiram, as princes of the congregation, were more distinguished than On the son of Peleth, and if they would have been won over to Moses, On would have followed their counsel; therefore Moses did not send for him. Thus On did not come, and was not present together with them [Dathan and Abiram], nor was he with Korach’s company; since he left him when Dathan and Abiram went away, while Moses was debating with Korach, and he never returned [to Korach’s company], because he changed his mind [after his original participation] on the advice of his wife who saved him, according to the words of our Rabbis. disciple!” For Scripture does not mention him [On] as one who was swallowed up [in the earth] together with Dathan and Abiram, nor was he among the company of those that gathered together against the Eternal who offered the incense, since there were two hundred and fifty men besides the four (Verse 2), and the fire which burnt those who offered the incense, destroyed two hundred and fifty men (further, Verse 35), it follows that On must have been saved. The death of Korach, Dathan, and Abiram, however, is expressly mentioned separately (ibid., Verses 27, and 32-33). mentioned at first.

ויאמרו לא נעלה, to be judged by you or your court. The expression עליה occurs frequently in conjunction with going to a court, to a judge. We find it in Deuteronomy 25,7 ועלתה יבמתו השערה, “his (the deceased’s) widow shall go up to the judges to protest her brother-in-law’s refusal to marry her.” It also occurs in this sense in Judges 4,5 where Boaz is reported as going up to the court to settle the matter of who will marry Ruth.