At the beginning of the Parshah, Rashi explains what led Korach to challenge Moshe and Aharon. He says that Korach envied the position of leadership that was granted to his cousin אליצפן בן עוזיאל, who was appointed Nasi of the family of Kehos.
Korach was a son of Yitzhar, who was the second son of Kehos ben Levi. Moshe and Aharon were sons of Amram, the eldest son of Kehos. Elitzafan was a son of Uziel, the fourth and youngest son of Kehos. Korach, therefore, reasoned that Moshe and Aharon had already received positions of leadership, and being that he was the son of the second son of Kehos, he was next in line for this position of leadership. Therefore, it seemed to him that he was skipped, whereby Elitzafan was appointed instead of him. Hence, Korach burned with jealousy of his cousin and the coveted position he was granted, which Korach believed was rightfully his.
Thereafter, Korach went all out against Moshe. He questioned the legitimacy of his leadership as well as the position of Kehuna Gedola for which Aharon Hakohen had been appointed.
Here, we see that jealousy was the root of this terrible conflagration which sowed such damage and confusion in Klal Yisroel. Therefore, we must study the nature of envy and the dire danger it presents.
Indeed, many seforim caution us regarding the destruction that gets caused by the trait of קנאה, jealousy. (עי' דברי יואל סוף קרח)