As for the sons of Merari The third and youngest son of Levi:
thou shalt number them after their families, by the house of their fathers; which is the form of expression used of them all; (See Gill on Numbers 4:2).
27
When Aaron commandeth and his sons, the sons of Gershon shall bear all things that pertain to the altar, the cords, and the vessels, or instruments, of their service; and all they shall know, to what charge they ought to be bound. (And when Aaron and his sons command, the sons of Gershon shall carry all the things that pertain to the altar, and the cords, and the vessels, or the instruments, of their service; and they all shall know, what each of them ought to carry.)
28
This is the office of the families of Gershonites, in the tabernacle of [the] bond of peace (This is the service of the Gershonite families in the Tabernacle of the Covenant); and they shall be under the hand of Ithamar, the son of Aaron, [the] priest.
29
Also thou shalt number the sons of Merari, by the families and houses of their fathers,
30
from thirty years and above unto fifty years, all that enter to the office of their service, and to the adorning of the bond of peace of witnessing. (from thirty years of age up to fifty years old, all who enter to serve in the Tabernacle of the Covenant, that is, in the Tabernacle of the Witnessing.)
31
These be their charges; they shall bear the tables of the tabernacle, and the bars thereof, the pillars, and their foundaments (and their foundations, or their bases);