Thematic Bible: Zeal against idolatry a cause of their appointment

Then Moses took his place at the way into the tents, and said, Whoever is on the Lord's side, let him come to me. And all the sons of Levi came together to him. And he said to them, This is the word of the Lord, the God of Israel: Let every man take his sword at his side, and go from one end of the tents to the other, putting to death his brother and his friend and his neighbour. And the sons of Levi did as Moses said; and about three thousand of the people were put to death that day.

Who said of his father, Who is he? and of his mother, I have not seen her; he kept himself separate from his brothers and had no knowledge of his children: for they have given ear to your word and kept your agreement. They will be the teachers of your decisions to Jacob and of your law to Israel: the burning of perfumes before you will be their right, and the ordering of burned offerings on your altar.