Jamieson, Fausset and Brown on Leviticus 27:30-33

30-33. all the tithe of the land, whether of the seed of the land--This law gave the sanction of divine authority to an ancient usage (Ge 14:20; 28:22). The whole produce of the land was subjected to the tithe tribute--it was a yearly rent which the Israelites, as tenants, paid to God, the owner of the land, and a thank offering they rendered to Him for the bounties of His providence. (See Pr 3:9; 1Co 9:11; Ga 6:6).