Why does it say "Malach Elokim Al Goyim"?
Rashi: Everyone will say so.
Radak: Until now Elokim was King only over Yisrael. Now He will be King over all nations.
Malbim: Until now described the beginning of the kingship; now it discusses the constancy of the kingship. "Elokim already ruled over the nations
Why does it say "Yashav Al Kisei Kodsho"?
Rashi: Now the throne is complete and greatness is understood, and they will tell that they were gathered to his city.
Radak: He is like a King on his throne; everything is underneath him and in his Reshus.
Malbim: Now He already sat on Kisei Kodsho - wondrous conduct b'Kodesh, above nature. He will no longer sit on the Kisei of Shamayim and the Ma'areches - "Hashem ba'Shamayim Hechin Kis'o" (103:19).