What does Numbers 3:14-39 mean?

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 these are the names of the sons of Gershon by their clans: Libni and Shimei. And the sons of Kohath by their clans: Amram, Izhar, Hebron, and Uzziel. And the sons of Merari by their clans: Mahli and Mushi. These are the clans of the Levites, by their fathers’ houses. To Gershon belonged the clan of the Libnites and the clan of the Shimeites; these were the clans of the Gershonites. Their listing according to the number of all the males from a month old and upward was 7,500. The clans of the Gershonites were to camp behind the tabernacle on the west, with Eliasaph, the son of Lael as chief of the fathers’ house of the Gershonites. 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. To Kohath belonged the clan of the Amramites and the clan of the Izharites and the clan of the Hebronites and the clan of the Uzzielites; these are the clans of the Kohathites. According to the number of all the males, from a month old and upward, there were 8,600, keeping guard over the sanctuary. The clans of the sons of Kohath were to camp on the south side of the tabernacle, with Elizaphan the son of Uzziel as chief of the fathers’ house of the clans of the Kohathites. 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 Eleazar the son of Aaron the priest was to be chief over the chiefs of the Levites, and to have oversight of those who kept guard over the sanctuary. To Merari belonged the clan of the Mahlites and the clan of the Mushites: these are the clans of Merari. Their listing according to the number of all the males from a month old and upward was 6,200. And the chief of the fathers’ house of the clans of Merari was Zuriel the son of Abihail. They were to camp on the north side of the tabernacle. 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; also the pillars around the court, with their bases and pegs and cords. 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, whom Moses and Aaron listed at the commandment of the LORD, by clans, all the males from a month old and upward, were 22,000.