(Bamidbar 18:30) "And you shall say to them (the Levites): When you separate its best part from it, (then it [i.e., what remains]) shall be reckoned to the Levites as produce of the threshing floor and as produce of the winepress."): This is an exhortation to the Levites to take (terumath ma'aser) only from its choicest. "then it shall be reckoned to the Levites as produce of the threshing floor and as produce of the winepress": Why is this stated? (i.e., it is already written [Ibid. 27]) Because it is written (27) "And your terumah will be accounted for you, etc.", I might think that since Scripture refers to it (first tithe) as "terumah," (viz. Ibid. 24), it retains its holiness forever; it is, therefore, written "then it shall be reckoned to the Levites as produce of the threshing floor and as produce of the wine press" — Just as with the produce of the threshing floor, one separates terumah, and what remains is chullin (non-terumah), so, with first tithe, he separates terumah (i.e., terumath ma'aser) and what remains is chullin. (Ibid. 31) "And you may eat it in every place": even in a cemetery.
For it would follow (otherwise), viz.: Since "terumah" (of a Cohein) is called "terumah," and first tithe is called "terumah," then if I have learned that terumah (of a Cohein) is to be eaten only in a (ritually) clean place, so, first tithe; it is, therefore, written "And you may eat it in every place" — even in a cemetery. "you and your household": to include an Israelite woman married to a Levite as permitted to depute (a messenger) to take terumah (i.e., terumath ma'aser, from her husband's first tithe). — But perhaps (this permits her) only to eat it! — Would you say that?
It follows otherwise, viz.: If she (a Cohein's wife) eats the "graver" — terumah, how much more so should (a Levite's wife) eat the "lighter" — ma'aser! It must mean, then, that an Israelite woman (married to a Levite) is permitted to be deputed to take terumah. (Ibid. 31) "For it is payment to you, in exchange for your service in the tent of meeting.": If he serves, he takes; if he does not serve, he does not take — whence it was ruled: If a Levite took upon himself every Levitical service except one, he has no portion in the Leviate. (Ibid. 32) "And you shall not bear sin because of it": And whence is it derived that if he did not separate (for terumath ma'aser) its choicest part, he does bear sin?
From "And you shall not bear sin because of it when you separate its best part from it." This tells me only of terumath ma'aser (i.e., what the Levi separates for the Cohein). Whence do I derive (the same for) terumah gedolah (i.e., what the Israelite separates for the Cohein)? From (Ibid.)
"And the holy things of the children of Israel you shall not profane and you shall not die." This is an exhortation to both the Levites and the Israelites.