Numbers 8:19 YLT

¹⁷  for Mine 'is' every first-born among the sons of Israel, among man and among beast; in the day of my smiting every first-born in the land of Egypt I sanctified them for Myself;

¹⁸  and I take the Levites instead of every first-born among the sons of Israel:

¹⁹  'And I give the Levites gifts to Aaron and to his sons, from the midst of the sons of Israel, to do the service of the sons of Israel in the tent of meeting, and to make atonement for the sons of Israel, and there is no plague among the sons of Israel in the sons of Israel's drawing nigh unto the sanctuary.'

²⁰  And Moses doth -- Aaron also, and all the company of the sons of Israel -- to the Levites according to all that Jehovah hath commanded Moses concerning the Levites; so have the sons of Israel done to them.

²¹  And the Levites cleanse themselves, and wash their garments, and Aaron waveth them a wave-offering before Jehovah, and Aaron maketh atonement for them to cleanse them,