Why does it say "Al Ken"?
Radak: When you will see and hear of Kel's ability and mastery over the nations, honor him with words of praise.
Malbim: This refers to verse 16 1 . So they will sing from the corners of the world - "Al Ken ba'Urim Kabdu..."
Verse 16 begins a new Parashah. It is a Chidush that our verse refers to it!
What are "ba'Urim"?
Targum Yonasan: In bringing light for Tzadikim. Rashi - this is for two tidings - the redemption from Bavel, and from Yishmael.
Rashi citing Menachem: They are cracks to which they fled. Also "b'Ur Kasdim" (Bereishis 11:28), he explained that it is a cavity. Every deep hole is called Ur (Rashi there). The same applies to "v'Al Me'uras Tzif'oni" (above, 11:8).
Radak: It is in valley, like "b'Ur Kasdim." Most of the cities were in valleys, and not in the mountains.
Malbim: Kindle lights for a sign of the salvation. The custom is, when there is a great salvation in the land, they illuminate with great lights the entire night to inform people far away.
Why does it mention islands?
Radak: They are far [from Yerushalayim. Even so, also they should honor Hashem.]
Malbim: They should illuminate with lights not only in Yehudah, rather, even on islands.
Why does it say "Elokei Yisrael"?
Radak: What He did to the nations was due to Yisrael.
Malbim: He showed His wonders to Yisrael.
