Last week's Torah portion (Shelach Lekha) told the tragic story about the "sin of the ten spies" and the divine decree that the generation of Israelites rescued from Egypt was sentenced to die while in the exile of the desert. In this week's portion (Korach), the hard truth of their condition began to sink in, and the people bemoaned their fate and rebelled further by attempting to overthrow God's designated leadership and return to Egypt. This rebellion was instigated and organized by Moses' cousin Korach, who – along with a band of co-conspirators – was swiftly judged and put to death, thereby vindicating the Aaronic priesthood and Moses' leadership of Israel.
Korach was the cousin of Moses and a well-respected Kohathite who was honored to be one of the carriers of the Holy Ark. He was a wealthy man of influence - a nassi (prince) of the people. Despite all this privilege, however, Korach rationalized that he should be the head of the Kohathite clan (instead of his cousin Elzaphan), since he was the firstborn of Kohath's second son (Izhar), whereas Elzaphan was not even a firstborn son. Because he felt slighted by Moses' choice, Korach went even further and brazenly questioned whether the office of the High Priest should not have been given to him – rather than to Aaron.
Korach's co-conspirators were two brothers named Dathan and Abiram from the tribe of Reuben, Israel's firstborn son. Together, they put together a force of 250 men to confront Moses and to challenge his exclusive claim to leadership: "You have gone too far! For all in the congregation are holy, every one of them, and the LORD is among them. Why then do you exalt yourselves above the assembly of the LORD?"
In response to their challenge, Moses proposed that Korach and his followers bring firepans to offer incense at the Tabernacle to determine whether they were indeed chosen to serve as priests. The following morning, when Korach and his 250 followers assembled at the gate of the Tabernacle to offer incense, God threatened to destroy them all instantly. Moses begged God not to destroy all the people, but only the rebels. He then warned the congregation to stand clear of the dwellings of Korach, Dathan, and Abiram. The earth then opened up and swallowed them alive, and a fire consumed the 250 men who illegitimately offered the incense...
Korach's rebellion introduced outright mutiny and chaos within the leadership of the camp that brought swift and terrible rebuke from the LORD. Nevertheless, the very next day the entire congregation of Israel audaciously began to accuse Moses and Aaron, saying: "You have killed the people of the Lord." When the people looked toward the Tabernacle, however, the Glory of the LORD appeared, where God descended to tell Moses and Aaron that he was going to destroy the Israelites for their treason. Despite Moses and Aaron's fervent intercession, however, a deadly plague broke out among the people. Moses then instructed Aaron to take his firepan with incense and to bring it in the midst of the congregation to make atonement for them. Aaron did so, "and he stood between the dead and the living; and the plague was stayed." The Torah tells us that 14,700 Israelites died because of the plague, not including the deaths of those involved in the rebellion of Korach.
As a final test to vindicate Aaron as God's chosen priest, each of the twelve tribal heads of Israel, as well as Aaron himself, were instructed to bring their staffs to Moses. Moses then inscribed their names on each staff and brought them into the sanctuary before the ark of the testimony. "And the staff of the man whom I choose shall sprout. Thus I will make to cease from me the grumblings of the people of Israel, which they grumble against you." The following day Moses went into the Tabernacle and "behold, the staff of Aaron for the house of Levi had sprouted and put forth buds and produced blossoms, and it bore ripe almonds." He then brought out all the staffs and gave them back to each of the tribal leaders. The LORD then told Moses to return Aaron's staff to the Tabernacle as a testimony for generations to come.
After all this transpired, the people began to dread the Presence of the LORD and the Tabernacle. To allay their fears, Moses gave them assurance that the sons of Aaron (i.e., the priests) and the Levites alone would bear responsibility for the sanctuary. But since the Levites and priests would receive no portion in the Promised Land, the people were instructed to generously support them by means of various gifts that are listed at the end of the Torah reading.