To what does "v'Amarta" apply?
Malbim: It applies also to verse 10; "Hashmen Lev ha'Am ha'Zeh" is a Ma'amar Musgar (parenthetical comment).
Why does it say "Shim'u Shamo'a"?
Rashi: I tell you to listen, and you do not heed to understand and see miracles that I did for you. You do not put to your heart to know Me.
Radak #1: "Shim'u" and "u'Re'u" are commands. The same applies to "Hashmen" (10). This is Hashem's way - when a sinner wants to sin, Hashem withholds from him the ways of Teshuvah, until he receives his punishment 1 . "Va'Yachazek Hashem Es Lev Pharaoh" (Shemos 9:12), and regarding Sichon "Ki Hiksheh Hashem Elokecha Es Rucho v'Imetz Es Levavo" (Devarim 2:30). It says about Bnei Eli "v'Lo Yishme'u l'Kol Avihem Ki Chafetz Hashem Lahamisam" (Shmuel I, 2:25).
Radak #2: Shim'u" and "u'Re'u" are command forms in place of the prefix to show second person. It is as if it says "Tishme'u? v'Sir'u." You hear the Navi's words of rebuke, and you do not understand. You see the Creator's wonders, and you do not know. I.e. you do not put to your heart and pay attention to Me. You intentionally fatten your hearts, make your ears heavy and plaster over your eyes, so you will not hear, see, understand or know. You do not desire Teshuvah or a cure, i.e. pardon after Teshuvah. So Yonason translates - you hear and do not look; you see and do not know.
Malbim: Yisrael's heart had regressed from accepting any matter of Chachmah and Musar. They did not want to hear the Navi's word at all. Hashem counseled Yeshayah to say Stam "hear" or "see", but not that they should understand or know, for then they would refuse to pay attention or see. They will make their ears heavy and close their eyes. Rather, say only "hear" or "see"; even so, if they hear, in the end they will put the matters to heart and understand, even though they did not intend for this, and repent.
I.e. Hashem commands them to make their hearts fat, in order that they will receive their punishment.
