What sort of Chilul is the Pasuk now referring o?
Rashi: It is referring to feeding Zarim Terumah. 1
Ramban #1: It is another warning against a Zar eating Kodesh. 2
Ramban #2: Based on the word "Yarinu", 3 it is a La'av against eating Tevel, together wit the punishment of Misah bi'Yedei Shamayim.
Ramban: There is no such La'av mentioned in the Gemara. Moreover, it is included in the La'av of "Lifnei Iver Lo Sitein Michshol", which incorporates all Isurim in the Torah.
Ramban: Because it wants to insert the punishment for the Kohanim who transgress (in Pasuk 16). And "b'nei Yisrael" is both the subject and the object ('The b'nei Yisrael should not desecrate the Kodshim of the b'nei Yisarel').
See R. Chavel's footnotes.
See Ramban, who elaborates further.
Why does the Torah write "Yarimu" (in the future).
Ramban (citing Sanhedrin, 83a): It adds an additional La'av for eating Tevel, from which Terumah is going to be taken.