Also verse 12 discussed returning from exile! Why is this repeated?
Radak: The matter is repeated to strengthen it.
Why will a great Shofar be sounded?
Radak: They will gather as if a Shofar was sounded in the entire world - "va'Shem Elokim ba'Shofar Yiska' (Zecharyah 9:14).
Who are "ha'Ovedim"?
Rashi: They are those who were scattered to a far land, past the Sambatiyon river.
Radak: They are the [10] tribes that Melech Ashur exiled. It is as if they were Avudim (lost) there, for they will not leave. Yehudah and Binyamin were in Galus Bavel, and returned after 70 years. Afterwards, they were exiled a second time [via Edom], and they are cast off in every corner and scattered.
Malbim: Those in Eretz Ashur are called Avudim, for they forgot their place and existence (essence) until the deadline for redemption. Those in Egypt were merely cast off.
Why does it mention "Mitzrayim"?
Radak: They will come until Egypt, and from there ascend to Yerushalayim.
What is "Har ha'Kodesh"?
Radak: It is Har ha'Moriyah, the place of the Beis ha'Mikdash.
