What is "b'Shovevi"?
Radak: At the time that I will return them from the nations to their land. Also "Leshovev Yakov Elav" (Yeshayah 49:5) refers to Hashavah (returning). Malbim ? they were not scattered among the Amim, so it suffices to return them.
What is the significance of "v'Kibatztim Osam me'Artzos"?
Malbim: From the Amim, they scattered to lands, and needed to be gathered.
How will Hashem be sanctified via Yisrael in the eyes of many Goyim?
Malbim: It will be via their good deeds and the miracles that He will do for them. This will cause their sin to be forgotten.
Why does it say "ha'Goyim Rabim"?
Radak: The noun has prefix Hei ha'Yedi'ah (to identify), but the adjective does not. We find like this ? "Suri ha'Gafen Nochriyah" (Yirmeyah 2:21), "ha'Agalah Chadashah" (Shmuel II, 6:3) and similar verses.