Why should they sound the Shofar in Tziyon?
Rashi: To make them hear that they should repent before this evil befalls them.
Malbim: Until now was a Nevu'ah of the decree of the locusts. Now discusses when the locusts began to come to the land. We sound Teki'ah for afflictions, to gather the nation. This should be in the entire city.
Why does it add "v'Hari'u b'Har Kodshi"?
Radak: The matter is repeated in different words. Tziyon is Har ha'Kodesh.
Malbim: Teru'ah is to arouse fear, so people will repent. This is in Har Kodshi, i.e. the Beis ha'Mikdash.
What is the significance of "Yirgezu Kol ha'Aretz"?
Malbim: They will fear Hashem.
What do we learn from "Ki Va Yom Hashem [Ki Karov]"?
Rashi: The day mentioned above, it came.
Malbim: We can say that a person's decree came only if it truly came; if not, a distance separates it. Regarding Hashem, if the time is close, we can say that it already came, for nothing blocks His decree.
