Ever wonder what the Bible is talking about when it mentions Zion?
No? Never? Really? . . . Wow. Well I have quite often and now finally I have found a really good explanation of it in Kenneth Gentry’s book, Postmillennialism Made Easy. Here is the relevant blurb from page 18 of his excellent book:
“But what does the Psalm  mean when it speak of this installation “on Zion”? Zion is an historical site: it is the Jebusite fortress David captures and renames the “City of David” (2 Sam 5:6–9). Since David’s bringing the Ark to Zion, the hill becomes sacred (2 Sam 6:10–12). Because of its significance in old covenant history, the name “Zion” gradually applies beyond the historical site to include Mount Moriah where Solomon builds the Temple (Isa 8:18; Joel 3:17; Mic 4:7). Eventually it covers all of Jerusalem (2 Kgs 19:21; Psa 48:2, 11–13; 69:35; Isa 1:8), even representing the whole Jewish nation (Isa 40:9; Zech 9:13).
Because of this, Zion becomes an image of God’s rule in the world. In the New Testament the images of Zion and Jerusalem transcend Old Testament realities, reaching to heaven itself (Gal 4:25–26; Heb 12:22; Rev 14:1). Thus, the New Testament sees the center of divine rule being transferred to heaven, where Christ currently rules over his kingdom (John 18:36; Rev 1:5).”