Bible Verses About The Levites: Zeal against idolatry a cause of their appointment

Then standing in the gate of the camp, he said: If any man be on the Lord's side, let him join with me. And all the sons of Levi gathered themselves together unto him:

And he said to them: Thus saith the Lord God of Israel: Put every man his sword upon his thigh: go, and return from gate to gate through the midst of the camp, and let every man kill his brother, and friend, and neighbour.

And the sons of Levi did according to the words of Moses, and there were slain that day about three and twenty thousand men.