And Korach, the son of Yitzhar... took (Bamidbar 38:1)
How can it be that an entire Torah portion derives its name from a wicked man who never repented of his misdeeds? Do not our Sages warn against even mentioning the name of an evil person?
One must therefore conclude that Korach possessed a positive quality from which we can learn and emulate. In fact, Korach's intense passion to serve as High Priest stemmed from his desire to draw as close to G-d as is humanly possible, an aspiration which in itself is pure. Furthermore, it is said that in the Messianic Era, the Levites (of which Korach was one) will ascend to the level of Kohanim.
Korach's error was that he wished to hasten the Redemption and enjoy its pleasures before it actually occurred, ignoring G-d's overall plan for mankind. His underlying motivation was, however, worthy of emulation. (the Rebbe)
For the whole congregation is holy, and G-d is within them (Num. 16:3)
Some Jews, when chided for not keeping Torah and mitzvot as stringently as they might, respond with the excuse, "but I have a Jewish heart! Deep inside where it counts I'm a good Jew." This was the argument of Korach and his supporters, who claimed that even though they didn't behave as they should, "G-d is within them" - deep inside they were good Jews. (Divrei Eliezer)
And Korach took [a bold step] and they rose up before Moses (Num. 16:1-2)
The Mishna states in Tractate Avot (5:17): "Which is a controversy that is not for the sake of Heaven? The controversy of Korach and all his faction."
The Mishna specifically avoids calling it a controversy between Korach and Moses, because even within Korach's group of 250 followers there was dissention, each one vying with the others for honor and glory. Indeed, this was a sure sign that their argument was not for the sake of Heaven. (Ye'arot Devash)