Why does the Brachah come from Tziyon?
Rashi: It is the gate of Shamayim.
Radak: It is the place of His Shechinah.
Malbim: From there Hashem commanded Brachah to the entire nation.
What is the significance of seeing "b'Tuv Yerushalayim"?
Rashi: You will rejoice in all the good.
Radak: You will see when Yisrael return to Yerushalayim from Galus.
Malbim: If you will strive for the good of the Klal, you will see the good of Yerushalayim and the success of the Klal.
What is "Kol Yemei Chayecha"?
Radak: You will see (have) good, both in Galus and in (after returning to) Yerushalayim. "U'R'e b'Tuv" applies also to this.
Malbim: You will designate all your days for the good of the Klal.