Numbers 4:16
And to the office of Eleazar the son of Aaron the priest pertaineth the oil for the light, and the sweet incense, and the daily meat offering, and the anointing oil, and the oversight of all the tabernacle, and of all that therein is, in the sanctuary, and in the vessels thereof.
Eleazar the son of Aaron was given charge of the oil for the light, and the sweet incense, and the daily meat offering, and the anointing oil, and the oversight of all the tabernacle, and of all therein in the sanctuary and in the vessels thereof. This charge was part of a deliberate and carefully ordered system in which sacred duties and responsibility for the sanctuary and its furnishings were assigned to designated workers rather than claimed.
Within that system the Levites were responsible for erecting and taking down the tabernacle and for carrying its sacred furnishings when Israel journeyed. Those appointed were to carry out their work with regard for its sacredness. Faithful Levite service in the appointed place was an honor, not a basis for claiming the priesthood or higher authority.
Tabernacle service was not left for any tribe or person to take up as they pleased. Each worker was to perform his own assigned work and leave other workers' responsibilities alone. God's arrangements for Israel were deliberate and orderly, and were to be followed rather than set aside by acting independently.