What is the meaning of "Heitivah bi'Rtzoncha Es Tziyon"?
Rashi: He will build the Beis ha'Mikdash there in the lifetime of my son Shlomo.
Radak: The last two verses of this Mizmor show that Ru'ach ha'Kodesh returned to David; they are a Nevu'ah for the future. He saw that the Beis ha'Mikdash will be destroyed, the first and second, due to sins. Even though they offered Korbanos constantly, since their deeds were evil, Hashem despised their Korbanos and destroyed the Mikdash. In the days of Mashi'ach, Korbanos will be accepted again, for all of Yisrael will have one heart to serve Hashem.
Malbim: Now Hashem does not desire Korbanos. This will change when He desires to dwell again in Tziyon.
What is the difference between Tziyon and Yerushalayim?
Malbim: Tziyon is the place of the Mikdash and Shechinah. Yerushalayim is the city itself, where the masses live. Hashem will benefit it via building its walls.
