Charles Spurgeon Commentary Numbers 4:29-32

"As for the sons of Merari, thou shalt number them by their families, by their fathers` houses; from thirty years old and upward even unto fifty years old shalt thou number them, every one that entereth upon the service, to do the work of the tent of meeting. And this is the charge of their burden, according to all their service in the tent of meeting: the boards of the tabernacle, and the bars thereof, and the pillars thereof, and the sockets thereof, and the pillars of the court round about, and their sockets, and their pins, and their cords, with all their instruments, and with all their service: and by name ye shall appoint the instruments of the charge of their burden." — Numbers 4:29-32 (ASV)

They had the heaviest load to carry, but they were the more numerous. They carried the solid columns upon which the covering of the tabernacle rested. And notice that they had also to carry the pins. Sometimes, God's servants dislike carrying pins. They feel themselves too big, but blessed is that servant who, in his place, can be content to carry their sockets, and their pins, and their cords, with all their instruments.