There are places in the Bible where God predicts, in words, what will happen: he talks about the future. But he also provides pictures, patterns, types, and models. In these cases he establishes an institution, or a rite, or a pattern of relationships. Then he drops hints, pretty soon a cascade of hints, that these pictures or patterns or types or models are not ends in themselves, but are ways of anticipating something even better. In these cases, then, God talks about the future in pictures.
Christians who read their Bibles a lot ponder the connections between the Davidic kingship and Jesus' kingship, between the Passover lamb and Jesus as "Passover Lamb," between Melchizedek and Jesus, between the Sabbath rest and the rest Jesus gives, between the high priest's role and Jesus' priestly role, between the temple the old covenant priest entered and the heavenly "holy of holies" that Jesus entered, and much more. Of course, for those who lived under the old covenant stipulations, covenantal fidelity meant adherence to the institutions and rites God laid down, even while those same institutions and rites, on the broader canonical scale, looked forward to something even better. Through these pictures, God talked about the future. Once a Christian grasps this point, parts of the Bible come alive in fresh ways.
One of these picture-models is Jerusalem itself, sometimes referred to as Zion (the historic stronghold). Jerusalem was bound up not only with the fact that from David on, it was the capital city (even after the division into Israel and Judah, it was the capital of the southern kingdom), but also with the fact that from Solomon on it was the site of the temple, and therefore of the focus of God's self-disclosure.
So for the psalmist, "the city of our God, his holy mountain" is not only "beautiful" but "the joy of the whole earth" (Ps. 48:1-2). It is not only the center of armed security (48:4-8), but the locus where God's people meditate on his unfailing love (48:9), the center of praise (48:10). Yet the psalmist looks beyond the city to God himself: he is the one who "makes her secure forever" (48:8), whose praise reaches to the end of the earth, for ever and ever (48:10, 14).
As rooted as they are in historic Jerusalem, the writers of the new covenant look to a "Jerusalem that is above" (Gal. 4:26), to "Mount Zion," to "the heavenly Jerusalem, the city of the living God" (Heb. 12:22), to the "new Jerusalem" (Rev. 21:2). Reflect long and often on the connections.
Numbers 11; Psalm 48; Isaiah 1; Hebrews 9