Thematic Bible: Zeal against idolatry a cause of their appointment

Then Moses stood in the gate of the camp, and said, Who is on the LORD'S side? let him come unto me. And all the sons of Levi gathered themselves together unto him. And he said unto them, Thus says the LORD God of Israel, Put every man his sword by his side, and go in and out from gate to gate throughout the camp, and slay every man his brother, and every man his companion, and every man his neighbor. And the children of Levi did according to the word of Moses: and there fell of the people that day about three thousand men.

Who said unto his father and to his mother, I have not seen him; neither did he acknowledge his brethren, nor knew his own children: for they have observed your word, and kept your covenant. They shall teach Jacob your judgments, and Israel your law: they shall put incense before you, and whole burnt sacrifice upon your altar.