The Medrash says, "Why did Korach rise up against Moshe? Because he saw the פרה אדומה - red heifer." The question is: What does the Parah Aduma have to do with the famous argument of Korach and his followers and why would this treasured mitzvah cause Korach to rebel against Moshe Rabbeinu's authority? 

     The famous Sephardic Gaon, R' Yehudah Albez zt"l explains that as we know, the בכורים - first-born sons, were supposed to have been the priests serving in the mishkan. They were originally chosen for this special service. However, due to their participation in the sin of the עגל הזהב - golden calf, this privilege was taken from them and given to the kohanim from the tribe of Levi, who refrained from worshipping the egel hazahav. Chazal tell us further that the Parah Aduma serves as an atonement for this sin of the golden calf. When Korach realized what the purpose of the פרה אדומה was for, he, therefore, reasoned that now that the sin had been atoned for, the rights of priesthood should return to the first-born. He maintained that Aharon and his children should not continue to practice the service that righfully belongs to him and the rest of the first-born sons of Bnei Yisroel. His mistake, obviously, was in his failure to realize that a sin is not atoned for in a single instant; rather, it involves a long, difficult process of forgiveness. Because of this shortsightedness on the part of Korach, he created a rift that shook the Jewish people to their very core.