Sforno on Numbers 5:9/ספורנו על במדבר ה׳:ט׳

1וכל תרומה, according to Sifrey 5 the t’rumah of which the Torah speaks here are the first fruit which have to be offered to G’d, as it is customary for the owner of fields or orchards to present these first fruit of each year’s produce (seven species) and to recite the appropriate benediction when presenting same in the Temple. (compare Deuteronomy 26,3). Here the Torah tells us that just as property stolen from a proselyte who died intestate, which was described as “being returned to G’d,” winds up in the hands of the priest, i.e. G’d’s agent, so the bikkurim, the farmer’s gift to G’d has also been assigned by G’d to the priest of the respective roster on His behalf.