Commentary for Numbers 18:31

בכל מקום AND YE MAY EAT IN EVERY PLACE — even in a cemetery (Sifrei Bamidbar 122).

כי שכר הוא לכם, חלף עבודתכם, "for it is a reward for you, in exchange for your service, etc." This is basically a repetition of what the Torah has already said about the tithes in verse 21. The Torah now added that these tithes do not possess a special sanctity as they may be eaten anywhere, as opposed to תרומה or similar gifts allocated to the priests. If someone sells the tithe, the money received is treated as totally secular. This is the message of the Torah writing that the tithes are given to the Levites as a reward for their service in the Temple, i.e. as some kind of wages.

V. 31. ספרי( אף בקבר :ואכלתם אותו בכל מקום וגו׳), während תרומה nur בטהרה gegessen werden darf (Wajikra Kap. 22), und ebenso דלא בעי חומה, dass es nicht wie מעשר שני nur in Jerusalem gegessen werden dürfe (Jebamot 86b). — אתם וביתכם sowie euch ist es, das מעשר, auch euren Frauen erteilt, und sind sie ebenso wie ihr berechtigt תרומת מעשר davon auszuscheiden und durch ihren Beauftragten ausscheiden zu lassen, לימד על נשואה בת ישראל שנותנת רשות לתרום (Jebamoth 86a).

אתם וביתכם “you and your households;” this includes the larger family, based on the patriarch of each family, who is considered the head within his tribe.

Our sages in the Sifri derive from that wording that only the Levites who have performed service in the Temple are entitled to such tithes. This leads the halachic authorities to arrive at the conclusion that any Levite who declared his preparedness to carry out all the duties a Levite has to perform bar one, is not considered as a true Levite. Both interpretations are fully legitimate.