Parashat Shemini begins on the last day of the ordination ceremony of Aaron and his sons as priests. Aaron’s sons, Nadav and Avihu, offer an alien fire to God . A fire comes from God, and both sons die immediately. Moses tells Aaron that the deaths of Nadav and Avihu demonstrate the responsibility of priests to do only what God has specifically commanded them. Moses calls on Aaron’s nephews to remove the bodies, and cautions relatives and the rest of the congregation not to mourn the deaths.

God commands Aaron and his sons not to drink intoxicants when they enter the Tent of Meeting, for them to be able to carry out their duties. God speaks to Moses and Aaron regarding the laws of kashrut. They are told that the Israelites are permitted to eat any mammal which has both a split hooves and chews its cud. The Israelites are permitted to eat any fish which has both fins and scales. A list of forbidden birds is given. Four-legged insects are forbidden unless they have a pair of jointed legs with which they can leap. The parasha ends with an affirmation of the special relationship between God and the people of Israel.

Some commentators explain that out of their joy of serving God, Nadav and Avihu brought an additional sacrifice.  If this were so, death seems an extreme, and even unjust, punishment. Hertz explains that they were punished according to their elevated status and that this was a warning to future priestly generations not to innovate their own sacrifices.