New Jerusalem is described as a city with walls. If this city were a cube, the walls would be superfluous. The wall would look like a maintenance slab on a modern building. This would, in turn, affect the remaining cube, reducing its size.

Also, a cube wouldn’t have the reflective value of a shining mountain where Christ’s glory provides the light (Rev. 21.23). The city is described as a “bride adorned” (Rev. 21.2), which would be an awkward description if it were a cube.

The bible doesn’t use any terms that could be thought of as a cube. Granted, the floor plan is pictured as “foursquared” (Rev. 21.16) with the height the same as each side dimension, but that does not mean a cubic structure. Neither is it a pyramid, for then anyone entering its gates would immediately start climbing since, in that case, the foursquare dimension would be its base. If the city is a pyramid with courtyard, then the pyramid would be rather slender with another, smaller foursquared base.

Many bible students want to compare this New Jerusalem to the Holy of Holies’ dimensions, given in scripture, by noting the cubic layout. I think this is wrong thinking since that place represented a mercy seat that only the Jewish High Priest could enter once a year to expiate Israel’s sins. It was a place apart from Israel where its holy furnishings were to be hidden and protected.

Presently, I believe, there is a temple in heaven which sketch God showed Moses at Sinai (Ex. 25.40). Mt. Sinai served as a meeting place between God and man furthering this idea that God and man dwell together on a mountain. Also, the believer’s hope enters within the veil of heaven (Heb. 6.19). This indicates that a temple still functions for Christians. Christ also went into the heavenly sanctuary with His own blood once for all (Heb. 9.11-12). Believers’ prayers now enter these holy places since we have the blood of Christ covering our sins (Heb. 10.19-20). Therefore, during this time, we still need a temple because of our inherent sin during the kingdom of darkness that still covers the earth (1Th. 5.4-8).

John’s vision of the New Jerusalem is set after evil is purged and a new heaven and earth established. There is no need for the former temple or its arrangements since we are no longer sinful nor in darkness. The text clearly says “no temple” (Rev. 21.22), which, I think, would include any rooms that the former temple had. At that blessed time, living water flows from the throne and we fellowship with the Lord face to face (Rev. 22.4). Therefore, the cubic dimensions of the Holy of Holies have no relevance since the temple provided a way for humans to expiate sin that, in the end time, is abolished.

Again, it is termed a “city” with at least one street. If it were a cube then the idea would be a large hollow room with all activity on the inside. This would resemble a square, glass-covered office building, albeit much bigger. So, are we to expect a cloistered room nearly 1400 miles high and square? Are there other descriptions elsewhere in scripture to guide us?

When John received the vision from the angel (Rev. 21.10-22.5), he was taken to a high mountain in the Spirit to behold a vision of the new city coming to the new earth. John mentions that the radiance was like a rare jewel which neither a cube or pyramid can reflect. Therefore, the layout resembles a jewel-encrusted mountain (probably gold, set with gems) where the glory of the Lord is reflected from many facets. Because the Lord’s throne is located in the city (Rev. 22.1) it must be set high on the mountain since the water is flowing from it. Perhaps, initially, the river forms waterfalls until it reaches the foothills and street of the city.

Most of the prophecies about the end times occur in the Old Testament and provide partial glimpses of Christ’s Kingdom. Several predictions refer to God’s eternal dwelling as a mountain.

David, in the Psalms, speaks of the Messianic King set on a holy mountain which ultimately has to refer to the perfected age of the new heaven and earth: As for me, I have set my King
on Zion, my holy hill (Ps. 2.6 ESV).

In Is. 2.2 the prophet speaks about the end-time Jerusalem (New Jerusalem): It shall come to pass in the latter days
that the mountain of the house of the Lord
shall be established as the highest of the mountains,
and shall be lifted up above the hills;
and all the nations [Gentiles] shall flow to it (ESV).

Jerusalem is situated on the central mountain ridge in Israel. In the Old Covenant it was mandated that all Israel males appear before the Lord in Jerusalem three times yearly during the redemptive festivals. A feature of the pilgrimages was songs of ascent where the worshippers sang Psalms to the Lord (Ps. 120-134). The fact that God chose a mountain as a pilgrmage place bolsters the idea that New Jerusalem is a mountain and not a cube or pyramid. Jeremiah speaks of the future blessed time of heavenly Jerusalem: At that time Jerusalem shall be called the throne of the Lord, and all nations shall gather to it, to the presence of the Lord in Jerusalem, and they shall no more stubbornly follow their own evil heart (Jer. 3.17 ESV).

Nebuchadnezzer’s Dream featured a Rock (cut out without hands) striking the Gentile idol so that no trace of it could be found (Dan. 2.31-35a). This Eternal Rock then increases to a mountain that fills the earth (Dan. 2.35b).

Micah 4.1-4 provides the fullest prophecy that God’s eternal abode resembles a glorious mountain: It shall come to pass in the latter days that the mountain of the house of the Lord
shall be established as the highest of the mountains,
and it shall be lifted up above the hills;
and peoples shall flow to it,
and many nations shall come, and say:
“Come, let us go up to the mountain of the Lord,
to the house of the God of Jacob,
that he may teach us his ways
and that we may walk in his paths.”
For out of Zion shall go forth the law,
and the word of the Lord from Jerusalem.
He shall judge between many peoples,
and shall decide disputes for strong nations far away;
and they shall beat their swords into plowshares,
and their spears into pruning hooks;
nation shall not lift up sword against nation,
neither shall they learn war anymore;
but they shall sit every man under his vine and under his fig tree,
and no one shall make them afraid,
for the mouth of the Lord of hosts has spoken (ESV).

This city features no temple since God will dwell with His people directly. I take this reference to God (Rev. 21.3) to be the Lord Jesus Christ since He is the radiance of the Father (Heb. 1.3). The Father Himself loves and dwells with us but will be invisible to us since Paul maintains that no one has seen Him or can see Him (1Tim. 6.16). Jesus has seen the Father of course (John 6.46).