Verse 1 already said "Al Tira." Why is this repeated?
Malbim: Yisrael were afraid for two reasons. (a) While in Galus, they feared lest they perish amidst the Nochrim. Therefore, it says "Al Tira
How is Hashem with us?
Radak: This can only discuss the future. According to what I explained that above refers to Sancheriv, it means, do not fear - just like I was with you in the past, I will be with you in the future.
Malbim: I will gather those of you who were scattered.
Why does it mention east and west?
Radak: I will gather your exiles from the four corners of the world. (Verse 6 mentions north and south.)
Why does it say "Zar'echa"?
Radak #1: Even the small ones, I will lead them slowly.
Radak #2: This Nevu'ah is for the future; those redeemed will be the descendants of those to whom this Nevu'ah was said.
What do we learn from "Akabetzeka"?
Radak: This refers to Techiyas ha'Mesim for those who will be in that generation, and they were exiled.
Malbim: The 10 tribes were exiled to the east. They are in one place, so they need not be gathered, just brought [back] to Eretz Yisrael. Yehudah and Binyamin were scattered to the four corners of the world; they must be gathered.
