What does this Mizmor discuss?
Rashi: It discusses the war of Gog and Magog. The nations will be agitated - "v'Zos Tihyeh ha'Magefah..." (Zecharyah 14:12).
Above, it says "Hashem Malach Tagel ha'Aretz", "Hashem Malach Af Tikon Tevel Bal Timot" (97:1, 96:10). Why does it say here "Hashem Malach Yirgezu Amim"?
Radak: The nations will be agitated and the land will slip when Gog and Magog fall. Afterwards, the land will rejoice and be established so it not falter; there will not be another war.
Malbim: Above it discusses Hashgachas Hashem via nature. He is like a king who dwells in Shamayim, for He conducts via the Ma'arachah. Now it depicts Him like [a king who] dwells on the land, between the Keruvim; He conducts miraculously via angels who do His will. They have wings - therefore it mentions the Keruvim. The land will slip amidst trepidation of the great King who dwells in it.
Why does it say "Yoshev Keruvim"?
Radak: Then He will return His Shechinah to Tziyon, in the Beis ha'Mikdash, and dwell between the Keruvim.
What is "Tanut"?
Rashi: This is [slipped], like "Natayu Raglai" (73:2).