Nadab and Abihu offer strange fire
Right after Aaron and his sons were ordained as priests, Aaron's sons Nadab and Abihu offered unauthorized fire and were struck dead.
Then Moses said to Aaron, “This is what Yahweh spoke of, saying, ‘I will show myself holy to those who come near me, and before all the people I will be glorified.’” Aaron held his peace.
Leviticus 10:3 (World English Bible)
The ordination ended gloriously: fire came from Yahweh and consumed the offering on the altar, and the people shouted and fell on their faces. But Nadab and Abihu, who had seen God's glory on Sinai, brought fire God had not commanded, and fire from Yahweh consumed them.
The lesson was sobering: the holy God must be approached his way. Hebrews later shows how Jesus, the perfect high priest, opens the way for us (Hebrews 10:19–22).
Dating notes
During the first month of the second year (Ussher, 1490 BC).