What is the meaning of "Nasach"?
Rashi #1: It is an expression of mixing, like "Maschah Yeinah" (Mishlei 9:2).
Rashi #2: It is an expression of authority; a spirit of sleep rules over you. He prophesized about Yisrael sinners who looked at the stars (relied on astrology).
Radak: He covered. This is like "veha'Masechah ha'Nesuchah" (25:7) and "Kesos ha'Nasech" (Bamidbar 4:7), a covering. I.e. He will cover you with sleep that He put on you, until you are considered like sleepers, that you do not hear one who calls you.
Malbim: He poured on you a spirit of sleep, as if you sleep amidst follies of this world.
What is "va'Y'atzem"?
Radak: He will close. The simple form is Otzem Einav (closing one's own eyes). He covered over you and closed your eyes so you will not see. And not only you, rather, [also] the false Nevi'im.
Malbim: It is as if He closed your eyes. You did not open them to see Hashem's actions.
Why does it say "v"Es Rasheichem ha'Chozim Kisah"?
Radak #1: They are the ones who closed your eyes until you do not see. It says "Nasach Aleichem Hashem" because the covering is so strong that it appears that it is from Hashem.
Radak #2: This is like "Hashmen Lev ha'Am ha'Zeh
