Numbers 4:38

And those that were numbered of the sons of Gershon, throughout their families, and by the house of their fathers,

The numbering of the sons of Gershon by their families and by the house of their fathers belongs to the larger numbering of the Levites for their appointed work connected with the tabernacle. It identifies the Gershonites according to family divisions and ancestral households as those set apart for that assigned service. That Levitical service was a position of honor bestowed upon the tribe. The honor consisted in erecting the tabernacle, encamping around it to guard and attend it, and carrying it with its sacred furnishings whenever Israel journeyed.