God had given specific instructions to Aaron’s sons, the priests for presiding over the various burnt offerings. On one occasion, Nadab and Abihu offered strange or profane fire on the altar. It is not known what made their fire different, but it is known that God was not pleased with the fire. Instead of accepting their sacrifice, He sent fire from heaven and “devoured” them. God demands true worship from His people today.
Aaron’s other sons, Eleazar and Ithamar were given more responsibilities following the death of their other brothers. They and their father were also given further instructions. Among those, was the prohibition of consuming strong drink when they went into the tabernacle.
Aaron was not permitted to publicly grieve for his sons, lest the people consider his grief as condoning his sons’ sin. In his private grief, he burned the sin offering instead of eating it. Upon hearing his reasoning, Moses was satisfied with his answer and accepted his feelings.