After Korach and his assembly are swallowed up by the earth for having challenged the leadership of Moshe and Aharon, the people complained again to Moshe and Aharon, saying “You have killed the people of G-d.” (Bamidbar 17:7) Even though the deaths of Korach and his assembly were obviously the result of a miraculous Divine intervention, the people blamed Moshe and Aharon, for they had instructed Korach and his followers to place fire and incense on their firepans and gather together. Immediately afterwards, they were swallowed up by the earth.
G-d reacts to their complaint by punishing them with a deadly plague. In order to halt the plague, Moshe instructs Aharon to take fire from the altar, combine it with incense in a firepan and bring it to the people who were being struck down. Since their transgression was challenging the right of Aharon and his sons to the Priesthood, it was only fitting that Aharon be the one to provide atonement for this challenge. Even though Moshe himself could have easily halted the plague, he wanted to make it known to the people that just as it was through the test of the firepans that Korach and his followers were punished, so too the remainder of the assembly would be rescued through the merit of Aharon and his firepan.
Aharon hastened and “stood between the living and the dead” as if he were telling the Angel of Death to skip over him. The plague ceased immediately, but not before more than 14,000 died almost instantaneously.
G-d saw, however, that the people still believed that Korach and his followers perished because they had brought an “unauthorized” fire, not because they had challenged Moshe and Aharon. He then ordered Moshe to perform another test to prove the pre-eminence of Aharon and his progeny. The leaders of each of the twelve tribes were instructed to bring identical staffs and to write their names on them, with Aharon writing his name on the staff of the tribe of Levi. The test would have two purposes: 1) To determine that the service in the Tabernacle was to be performed by the Levites, and not by the firstborns. 2) To determine that Aharon, and not another Levite, would serve as the High Priest.
Aharon’s staff was the only one that blossomed: “It brought forth a blossom, sprouted a bud and almonds ripened.”(Bamidbar 17:23) The word for “bud” in Hebrew is the word “tzitz”, which is also the word for the most important of the garments worn by the High Priest. This was a clear indication that Aharon deserved that office. The word for “almonds” is “shekadim”, which is closely related to the word “shekaid”, which can mean “diligence” or “perseverance”. This is an indication that his offspring would persevere forever in that service.
There were also four miracles associated with Aharon’s staff: 1) A dry, lifeless staff blossomed. 2) The blossom preceded the bud. 3) The bud was the first indication of the fruit. 4) The staff produced fully-ripened almonds overnight.
The whole process was contrary to nature, since normally when the fruit appears the blossom falls off. In this case, miraculously, the blossom, fruit bud and ripened fruit all appeared together.
With this test the people realized that Korach and his assembly died because they had infringed on the “territory” which belonged rightfully to Aharon and his sons. Consequently, they cried out “Behold! We perish, we are lost; we are all lost! Everyone who approached closer to the Tabernacle of G-d will die! Will we ever stop perishing?” (Bamidbar 17:27-28) That is to say, they were afraid that it was inevitable that they would end up coming into contact with one of the holy vessels of the Tabernacle and would perish as a result. Therefore, Aharon is told that he is responsible to guard the Tabernacle with vigilance to prevent this from occurring.