Why does it say "va'Yashev"?
Radak: This is past tense used in place of future; this is common in Nevu'ah. He will save me from them and return on them the evil that they did.
Malbim: The Resha'im's punishment will not be from something external to them. Rather, the evil itself will cut them off.
What is "Onam"?
Rashi: Their Ones (coercion), like "Yitzpon l'Vanav Ono" (Iyov 21:19).
Radak: This is like "Amal va'Aven" (10:7), even though here the Vov is not heard (as a consonant). Similarly, sometimes the Vov is Avlasah is heard, and sometimes it is not heard.
Why does it repeat "Yatzmisem"?
Radak: It is to strengthen the matter.
Malbim: (a) "Yatzmisem Hashem Elokeinu" teaches that it will not be via nature - "Tav'u Goyim b'Shachas Asu...; Noda Hashem Mishpat Asah" (9:16-17). (b) The verse teaches that they will be cut off for two reasons - due to their evil, and because He is Elokeinu, who supervises over us and wages our battle against oppressors.
