Why does it say that Hashem loves "Sha'arei Tziyon"?
Radak (7, from Shocher Tov): He endears Batei Kenesiyos and Batei Midrash. Whom does He endear most? Tziyon, His palace.
Malbim: The nations said that this shows that Hashem does not love Yisrael, and did not put his Shechinah among them due to them. If he did, he would have accepted their Avodah in all Mishkenos Yakov! Rather, He loves only Sha'arei Tziyon.
Why does it say "Sha'arei" (plural)?
Radak: The Zekenim and Chachamim sit in the gates - "ha'Sha'arah El ha'Zekenim" (Devarim 25:7), "ha'Am Asher ba'Sha'ar veha'Zekenim" (Rus 4:11).
Why does it say "mi'Kol Mishkenos Yakov"?
Radak: Hashem loves all Mishkenos Yakov - "Mah Tovu Ohalecha Yakov Mishkenosecha Yisrael" (Bamidbar 24:5). Even so, He loves Sha'arei Tziyon more, for the Chachamim and those who engage in Avodas Hashem are there.
