Numbers 18:28 - Clarke's commentary and critical notes on the Bible

Thus ye also shall offer an heave offering unto the LORD of all your tithes, which ye receive of the children of Israel; and ye shall give thereof the LORD'S heave offering to Aaron the priest. Thus ye also shall offer a heave-offering - As the Levites had the tithe of the whole land, they themselves were obliged to give the tithe of this tithe to the priests, so that this considerably lessened their revenue. And this tithe or tenth they were obliged to select from the best part of the substance they had received, Numbers 18:29, etc. A portion of all must be given to God, as an evidence of his goodness, and their dependence on him. See the end at Numbers 20:28.