And the LORD spoke to Moses in the wilderness of Sinai, saying, “List the sons of Levi, by fathers’ houses and by clans; every male from a month old and upward you shall list.” So Moses listed them according to the word of the LORD, as he was commanded. And these were the sons of Levi by their names: Gershon and Kohath and Merari….
And the guard duty of the sons of Gershon in the tent of meeting involved the tabernacle, the tent with its covering, the screen for the entrance of the tent of meeting, the hangings of the court, the screen for the door of the court that is around the tabernacle and the altar, and its cords; all the service connected with these…
The clans of the sons of Kohath were to camp on the south side of the tabernacle…And their guard duty involved the ark, the table, the lampstand, the altars, the vessels of the sanctuary with which the priests minister, and the screen; all the service connected with these.
And the appointed guard duty of the sons of Merari involved the frames of the tabernacle, the bars, the pillars, the bases, and all their accessories; all the service connected with these….
Those who were to camp before the tabernacle on the east, before the tent of meeting toward the sunrise, were Moses and Aaron and his sons, guarding the sanctuary itself, to protect the people of Israel. And any outsider who came near was to be put to death. All those listed among the Levites, who Moses and Aaron listed at the commandment of the Lord, by clans, all the males from a month old and upward, were 22,000.
And the Lord said to Moses, “List all the firstborn males of the people of Israel, from a month old and upward, taking the number of their names. And you shall take the Levites for me – I am the Lord – instead of all the firstborn among the people of Israel, and the cattle of the Levites instead of all the firstborn among the cattle of the people of Israel.”
And the Lord spoke to Moses, saying, “I am the Lord. And as the redemption price for the 273 of the firstborn of the people of Israel, over and above the number of the male Levites, you shall take five shekels per head; and give the money to Aaron and his sons as the redemption price for those who are over.” So Moses took the redemption money from those we were over and above those redeemed by the Levites. (Numbers 3:14-51, ESV)
Yahweh breaks down the responsibilities for care of the tabernacle between the three clans of Levi, each one taking a portion of the tent that they were responsible for setting up, taking down and transporting when God said it was time to move. Aaron and his sons guarded the entrance.
Then God has Moses number all the Levites and their cattle so they can substitute for all the firstborn sons of Israel and the firstborn of their cattle. But there are not enough Levites in all to cover the number of all the Israelite firstborns from the other tribes. So the difference is paid to Aaron with the redemption price for the 273 extra firstborns in Israel.
As Israel’s firstborn belong specially to Yahweh, devoted to His service, so Jesus, the ultimate “Firstborn” is devoted to the Father’s service. His service is to pay the redemption price for all of God’s people. The overage has been covered. What we could not cover to redeem ourselves He has covered with his eternal and inestimable sacrifice.