Peter Pett's Commentary on the Bible
Numbers 4:21-28
The Responsibility of the Sons of Gershon (Numbers 4:21).
‘And Yahweh spoke to Moses, saying, “Take the sum of the sons of Gershon also, by their fathers' houses, by their families, from thirty years old and upward until fifty years old you shall number them, all who enter in to wait on the service, to do the work in the tent of meeting.” '
Yahweh's next command was to take the sum of the Gershonites. Again it was to be done by their father's houses (‘thousands?') and by their families (‘hundreds'?). All males who were between 30 and 50 who were fit for service were to be numbered, those who could respond to the call to work in the Tent of Meeting.
“ This is the service of the families of the Gershonites, in serving and in bearing burdens.”
The way in which the Gershonites were to serve was now listed. It was stressed that their service included the bearing of heavy burdens.
“ They shall bear the curtains of the tabernacle, and the tent of meeting, its covering, and the covering of dolphin skin that is above upon it, and the screen for the door of the tent of meeting, and the hangings of the court, and the screen for the door of the gate of the court, which is by the tabernacle and by the altar round about, and their cords, and all the instruments of their service, and whatever shall be done with them. In these things shall they serve.”
It was their responsibility to carry the Dwellingplace itself with its curtains and accoutrements, its door screen and gate screen, and its dolphin skin covering. Elsewhere we learned that the Levites were to dismantle the Dwellingplace when a journey was to begin and re-erect it at the next stop (Numbers 2:51). Probably all three sub-tribes assisted with this dismantling and erecting.
“ At the commandment of Aaron and his sons shall be all the service of the sons of the Gershonites, in all their burden, and in all their service; and you shall appoint to them in charge all their burden.”
All their service and work and burden bearing was to be done under the authority of Aaron and his sons who were to direct who would do what.
“ This is the service of the families of the sons of the Gershonites in the tent of meeting, and their charge shall be under the hand of Ithamar the son of Aaron the priest.”
So the service of the ‘families' of the sons of the Gershonites has been made clear. And while about their activity, and on the march, they were under the supervision and control of Ithamar, the son of Aaron ‘the Priest' (the High Priest).