Numbers 7:8

And four wagons and eight oxen he gave to the sons of Merari,
&c.] All the remaining wagons and oxen, which were double the number given to the Gershonites:

according unto their service;
being much heavier than theirs, having all the boards, pillars, sockets, pins; cords to bear and carry: thus Moses was directed of God wisely to dispose of those carriages, in proportion to the services each was employed in; and in a spiritual way, as the day, duty, and service of the people of God be, he proportions grace and strength to them to answer thereunto:

under the hand of Ithamar the son of Aaron the priest;
under whose care, inspection, and direction, were both the Gershonites and Merarites, ( Numbers 4:28 Numbers 4:33 ) ; and by whom were delivered, according to the instruction of Moses, the several wagons and oxen, to them.