Numbers 3 (résumé): The Levites

This chapter initially reminds us that Aaron and his sons Eleazar and Ithamar served as priests in the Tabernacle as the other sons Nadab and Abihu had been killed for offering a sacrifice with unauthorized fire. Now, however, God chose the tribe of Levi to assist Aaron in caring for the Tabernacle and serving God in it. The Levites were set apart from the rest of Israel and dedicated to the work of the Lord, and God counted the Levites in place of the firstborn of Israel. So God told Moses to count the Levites by their families and clans counting every male a month old or more. And the Levites were divided into 3 groups: the Gershonites, the Kohathites and the Merarites. 

The Gershonites totalled 7,500 males and were told to camp on the west side of the Tabernacle and be responsible for the Tabernacle coverings and hangings around the courtyard.

The Kohathites totalled 8,600 males and were told to camp on the south side of the Tabernacle and be responsible for the Ark of the Covenant, the gold table, the lampstand, the altars and all the vessels of the Tabernacle.

The Merarites totalled 6,200 males and were told to camp on the north side of the Tabernacle and be responsible for the frames of the Tabernacle, its cross-bars, posts, bases, posts tent pegs and ropes. 

Moses, Aaron and his sons and their respective families camped on the east side of the Tabernacle.

So God counted the 22,000 Levites as his exclusive servants in the place of the 22,273 firstborn of Israel and the difference was paid @ 5 shekels a head paid by the Israelites to Aaron and his sons. (There are some difficulties with the mathematics of this chapter)