Albert Barnes Commentary Numbers 18:23

"But the Levites shall do the service of the tent of meeting, and they shall bear their iniquity: it shall be a statute for ever throughout your generations; and among the children of Israel they shall have no inheritance." — Numbers 18:23 (ASV)

Bear their iniquity - The words probably refer to the iniquity of the people; who, if they had approached the tabernacle, would have fallen, from their proneness to transgress, into overt acts of offence. Against such a result they were, through the ministrations of the Levites, mercifully protected. .