Why will they be called "Am ha'Kodesh"?
Malbim: It is due to the Kedushah of their deeds and their virtue.
Why will they be called "Ge'ulei Hashem"?
Malbim: It is due to the miracles that will be done for them.
What is the significance of calling Tziyon "Derushah"?
Radak: This is opposite to before - "Tziyon Hi Doresh Ein Lah" (Yirmeyah 30:17).
Malbim: Hashem always seeks it.
What is the significance of calling it "Ir Lo Ne'ezavah"?
Radak: This is opposite to what you said - "Azavani Hashem" (49: 14).
Malbim: Hashem never abandoned it. His Hashgachah did not depart even when it was destroyed. Its destruction was for a limited time to finish off [punishment for] sin.