Numbers 4:24

This is the service of the families of the Gershonites, to serve, and for burdens:

This is the service appointed to the families of the Gershonites, to serve in the tabernacle and to carry its burdens. Their particular share was the care of the curtains and hangings, both in the settled camp and in transport during travel. That work belonged to the broader duty of the Levites to erect the tabernacle and encamp around it, and when Israel journeyed to take it down and carry it with its sacred furnishings, then to set it up again when the camp moved.

The assignment was part of an orderly system established by God in which each family had its appointed place and responsibility. Sacred work was not left for any tribe or person to choose individually, nor to be performed indiscriminately.