Why did David compose this Mizmor?
Malbim: The previous Mizmor concluded with Hashem's Hashgachah to Tziyon. This entire Mizmor is about this.
Who should praise Hashem?
Radak: The entire world. When "Hashem Yimloch l'Olam", all will recognize His kingship, and their song and praise will be pleasant.
What is the meaning of "Ki Tov Zamrah"?
Rashi: It is good to sing to him.
Malbim: Zemer is a higher level than Tehilah. It is for extra benefits that Hashem did, so it is appropriate for Elokeinu (refer to 147:1:4:1). Tov refers to the true good found in a matter itself. Tehilah is for habitual benefits.
Why does it say "Elokeinu"?
Malbim: This hints to Hashem's connection to Yisrael and His Hashgachah Pratis over them.
What is "Navah"?
Radak: This is like Na'eh (pleasant).
Malbim: It refers to the beauty of the order of conduct that Hashem made.
