THE LEVITES BECOME PRIESTS

Midrash Rabbah - Numbers 4:8

TAKE THE LEVITES, etc. (Numbers 3:45).

… God said to them: ' I have given promotion to the firstborn having made them great in the world and they have renounced Me and have risen and offered sacrifices before the Calf. Behold, I shall dismiss the firstborn and enroll the sons of Levi.’ Therefore the Holy One, blessed be He, told Moses to number them; as it says: ‘Number the children of Levi’ (Numbers 3:15).