Why does it say "Kra v'Garon"?
Radak: Hashem tells the Navi to call loudly to his generation. They showed themselves to be good, but they were evil. He rebukes them for their deeds. Calling is in the throat, even though the speech is articulated in the mouth - "Romemus Kel bi'Gronam", "b'Kar'i Nichar Geroni" (Tehilim 149:6, 69:4).
Why does it say "Al Tachsoch"?
Radak, Malbim: Constantly call to them.
What is the comparison to a Shofar?
Rashi: He raises his voice at them like a Shofar, which is heard from afar.
Malbim: (a) Your voice should keep getting stronger, like a Shofar 1 . (b) A Shofar is merely sounds the blowing of the one who blows it. So the Navi is a Kli via which Hashem speaks. (c) A Shofar makes a broken sound, arouses trembling and reminds people to repent. (So your voice should do!)
Does Malbim refer to the Shofar of Matan Torah, which kept getting stronger? When a human blows, it gets weaker (Rashi Shemos 19:19)! (PF)
Why does it say "Ami" and "Beis Yakov"?
Rashi: Ami refer to Chachamim. Their Shogeg sins are considered Pesha (intentional), for 'forgetting learning is considered Mezid' (Avos 4:13). Beis Yakov refers to ignoramuses. Even their intentional sin is considered Shogeg.
Malbim: Pesha are sins of rebellion - they are attributed to Ami, i.e. Bein Adam la'Makom. Chata'im are sins due to being Beis Yakov, i.e. Bein Adam l'Chavero 1 .
Indeed, one does not sin Bein Adam l'Chavero in order to rebel against Hashem. However, Chet is Shogeg. This applies equally Bein Adam l'Chavero and Bein Adam la'Makom! (PF)
