Why does it say "Nemogim Eretz v'Chol Yosheveha"?
Rashi: On the day of Matan Torah, the entire world feared the condition that Hashem with the creation, that if Yisrael will not accept the Torah, [the creation] will revert to be void (Shabbos 88a).
Radak: [When Hashem will redeem Yisrael,] all inhabitants of the world will tremble amidst fear of the vengeance of Yisrael.
Malbim: Refer to 75:3:2:3.
Who is "Anochi"?
Rashi: It is Your nation, Yisrael.
Radak: It is Hashem.
Malbim: It is straightness (personified).
What is the meaning of "Tikanti Amudeha"?
Rashi: When I said "Na'aseh v'Nishma" (Shemos 24:7; this enabled the continued existence of the world - refer to 75:4:1:1).
Radak: Then, all will recognize that I prepared the pillars [of the world] - based on My will, it stands or melts. "Amudeha" are the mountains. This is a metaphor, like "Por Hisporerah Eretz" (Yeshayah 24:19).
Why does it say "Selah"?
Malbim: This completes the matter, the first speech of straightness.