Numbers 4:28
This is the service of the families of the sons of Gershon in the tabernacle of the congregation: and their charge shall be under the hand of Ithamar the son of Aaron the priest. This is the service of the families of the sons of Gershon in the tabernacle of the congregation: and their charge shall be under the hand of Ithamar the son of Aaron the priest.
The families of the sons of Gershon had a defined, assigned share in the service of the tabernacle of the congregation, a distinct portion of the sacred work entrusted to them. That assigned work included the care of the curtains and hangings of the tabernacle. Their charge was to be carried out under the hand of Ithamar, the son of Aaron the priest, with their service placed under his authority and supervision.
The arrangement reflects careful divine ordering of the tabernacle service through division among appointed groups, with designated families and officers each responsible for its assigned task. Duties of this kind were set by God rather than left to individual choice, performed indiscriminately, or claimed through ambition.