Charles Ellicott Commentary Numbers 8:26

"but shall minister with their brethren in the tent of meeting, to keep the charge, and shall do no service. Thus shalt thou do unto the Levites touching their charges." — Numbers 8:26 (ASV)

To keep the charge. —A clear distinction is here made between the service which involved heavy manual labour in carrying the furniture of the Tabernacle and in slaughtering the victims, and the charge or oversight of the furniture and the vessels of the Sanctuary.