What is the meaning of "Nora Hashem Aleihem"?
Radak #1: Hashem, who is Nora (awesome), was on them, i.e. on Am Hashem mentioned (at the end of the previous verse). This is like Targum Yonasan - fear of Hashem said to redeem them.
Radak #2: Aleihem refers to the nations. A time will come when Hashem will be awesome on them, and they will fear Him and [fear] to harm His nation.
Why does it say "Ki Razah Es Kol Elokei ha'Aretz"?
Rashi: They became weak. Radak - via this, all will recognize that only Hashem is G-d - "v'Hayah Hashem l'Melech Al Kol ha'Aretz" (Zecharyah 14:9). Razah is like "va'Yshalach Razon b'Nafsham" (Tehilim 106:15) - He will nullify them and cease people's belief in them.
Why will they bow to Hashem?
Rashi: They will see that their gods were ruined.
Malbim: They will see that there is no real [power] to idols.
