For every firstborn among the Israelites is Mine, both man and animal. I consecrated them to Myselfa on the day I struck down every firstborn in the land of Egypt.
But I have taken the Levites in place of every firstborn among the Israelites.
From the Israelites, I have given the Levites exclusively to Aaron and his sons to perform the work for the Israelites at the tent of meeting and to make atonement on their behalf, so that no plague will come against the Israelites when they approach the sanctuary."b20
Moses, Aaron, and the entire Israelite community did [this] to the Levites. The Israelites did everything to them the Lord commanded Moses regarding the Levites.
The Levites purified themselves and washed their clothes; then Aaron presentedc them before the Lord as a presentation offering. Aaron also made atonement for them to ceremonially cleanse them.
After that, the Levites came to do their work at the tent of meeting in the presence of Aaron and his sons. So they did to them as the Lord had commanded Moses concerning the Levites.
The Lord spoke to Moses:
"In regard to the Levites: From 25 years old or more, a man enters the service in the work at the tent of meeting.d25
But at 50 years old he is to retire from his service in the work and no longer serve.
He may assist his brothers to fulfill responsibilitiese at the tent of meeting,f but he must not do the work. This is how you are to deal with the Levites regarding their duties."