"There are some conclusions which the Holy Spirit would mark indelibly upon our minds. One of these is the fact that the mount Zion of John’s vision is not the literal, physical, earthly mount Zion. Look to the Middle East, to the mount Zion in the earthly Jerusalem. Do we see the glorified Lamb of God standing there? Has He ever been seen standing there at any time during the past two thousand years? Absolutely not! Nor is the Lamb of God going to stand visibly again in flesh on that earthly mount Zion. Why should He? “For ye are not come unto the mount that might be touched…but ye are come untomount Zion…the heavenly Jerusalem” (Heb. 12:18,22). Jesus Christ Himself is the chief cornerstone in the spiritual house of God raised up upon the heavenly mount Zion! “Wherefore also it is contained in the scripture, Behold, I lay IN ZION a chief corner stone, elect, precious: and he that believeth on Him shall not be confounded” (I Pet. 2:6). And again, “Why do the heathen rage, and the people imagine a vain thing? The kings of the earth set themselves, and the rulers take counsel together against the Lord, and against His Christ. For of a truth against Thy holy child Jesus, whom Thou hast anointed, both Herod, and Pontius Pilate, with the Gentiles, and the people of Israel, were gathered together. For to do whatsoever Thy hand and Thy counsel determined before to be done. He that sitteth in the heavens shall laugh: the Lord shall have them in derision. Yet have I set my king upon my holy hill of Zion. I declare the decree: Thou art my Son, this day have I begotten Thee” (Ps. 2:1-7; Acts 4:25-28). To this heavenly and spiritual mount Zion come the 144,000 who “follow the Lamb whithersoever He goeth.” Can we not see by this that the mount Zion that John saw in his vision was a “sign.” It signified, symbolized, the invisible heavenly mount Zion; and that is where the firstborn Son of God has been laid as the chief cornerstone! And it is there upon the heavenly, spiritual mount Zion that the 144,000 overcomers follow the Lamb!"
This is a great study on spiritual Zion:
"How appropriate that our Lord Jesus should be standing on the heavenly, spiritual mount Zion! Why should this be? Because his forefather, King David, captured the earthly mount Zion, and the citadel upon it came to be called “the city of David” (II Sam. 5:4-9). The earthly is but the picture, the type, the shadow of the heavenly! His standing there indicates that He has begun to reign, that the king has taken His power. And now John beholds 144,000 following the Lamb to the summit of the heavenly, spiritual mount Zion! Fail not to observe that it is not simply “mount Zion,” but rather “the mount Zion,” signifying the spiritual, even the heavenly — the unique, abiding, eternal mount of the Lord. The literal, earthly mount Zion is still in the earthly Jerusalem in the land of Israel, but it is merely a type. The mount Zion of the Revelation is a spiritual mountain! This Zion realm IS NOT A CERTAIN GEOGRAPHICAL LOCATION. But it is in certain geographical locations! A place doesn’t make Zion — Zion makes the place itself — ZION! The “place” of Zion is within a people, in the spirit. Man doesn’t create Zion, Zion is the Christ manifested in all His fullness! The new creation man has come to mount Zion. Mount Zion represents a spiritual reality and attainment that is available to us right now in the realm of the spirit! It’s a spiritual place, a spiritual identity, a spiritual administration, and a spiritual state of being."