Which Goyim does this address?
Radak: It is the families who will come to the Beis ha'Mikdash when you (Yisrael) return to your land.
Malbim: It is those who think that Hashem created the world, but handed over His kingship and conduct to generals and powers of nature.
Why does it say "Hashem Malach" (past tense)?
Rashi: They will sing so in the future (Hashem already became king).
Radak: They will recognize His kingship, for He took His nation out of Galus with great honor. Even their [former] rulers took them to their land, they will see that He rules over everything, and kingship is His. They will recognize the Mishpat that He did to the Goyim who came against Yerushalayim.
Malbim: They will recognize that also natural conduct is totally hidden miracles. He arranged nature so that also Mishpat will be found also Mishpat for reward and punishment. Nature does not conduct the world alone; refer to 96:10:3:2.
What is the meaning of "Af Tikon Tevel Bal Timot"?
Radak: The entire world will be b'Shalom. "Lo Yisa Goy El Goy Cherev Lo Yilmedu Od Milchamah" (Yeshayah 2:4).
Malbim: Even though Hashem established fixed natural laws that never falter, with His Chachmah He arranged that nature will agree with Hashgachah according to deeds. Even though the land is established on natural laws, He judges nations for reward or punishment. Natural laws are drawn after people's actions - "v'Hayah Im Shamo'a Tishme'u El Mitzvosai v'Nasati Matar Artzechem" (Devarim 11:14), "Pen Yifteh Levavchem...; v'Atazar Es ha'Shamayim" (ibid., 16-17).
What is the meaning of "Yadin Amim b'Meisharim"?
Rashi: He will judge for merit those whom He will reverse to a clear language [to serve Him - Tzefanyah 3:9].
Radak: He will judge the nations straightly, and the Resha'im among them will be finished off.
