John Wesley on Leviticus 27:21

When it goeth out - That is, out of the possession of the other man to whom the priest sold it. The possession shall be the priests - For their maintenance. Nor is this repugnant to that law, that the priests should have no inheritance in the land, Num 18:20, for that is only spoken of, the tribe of Levi in general, in reference to the first division of the land, wherein the Levites were not to have a distinct part of land, as other tribes had; but this doth not hinder, but some particular lands might be vowed and given to the priests, either for their own benefit, or for the service of the sanctuary.