The length, width and height of the New Jerusalem are all the same, suggesting a perfect cube (Rev. 21:16). But there is another shape whose length, width and height are the same, and that is the pyramid. There is nothing in the description of the New Jerusalem in Revelation that requires either a cube or a pyramid? So how should we decide? Should we envision the New Jerusalem as a cube or as a pyramid?
Most interpreters envision the New Jerusalem as a cube and, in my view this is probably correct. A cube has twelve edges, but a pyramid has only eight. The description of the New Jerusalem makes abundant use of the number twelve and never uses the number eight. The New Jerusalem has twelve gates, twelve foundations, walls 144 cubits high, and dimensions measuring 12,000 stadia (Rev. 21:12-21). This wide-spread use of twelve coheres with the major use of twelve elsewhere in Revelation and the New Testament. It is the number of God’s people and the city becomes the bride of Christ when it is filled with saved humanity. While the text does not specify the shape, a cube would be consistent with the symbolism of Revelation.
What is theologically significant about the cube is that the only other cube in the Bible is the Most Holy Place of the Old Testament temple (1 Kings 6:20). Its sides and height were completely equal. The New Jerusalem, then, is modeled on the Most Holy Place. What is forbidden to all but the High Priest in Old Testament times is now open to all the redeemed. Relationship with Christ elevates all to the roles of kings and priests. All have face to face engagement with God (Rev. 22:4) in the heavenly Most Holy Place, the New Jerusalem.