Numbers 8:17 "For every firstborn among the sons of Israel is Mine, among the men and among the animals; on the day that I struck down all the firstborn in the land of Egypt I sanctified them for Myself.
Numbers 8:19 "I have given the Levites as a gift to Aaron and to his sons from among the sons of Israel, to perform the service of the sons of Israel at the tent of meeting and to make atonement on behalf of the sons of Israel, so that there will be no plague among the sons of Israel by their coming near to the sanctuary."