How are we to understand the wall’s measurement?

If the city was a cube, the wall John saw would have been 12,000 stadia high, and so the 144 cubits would need to represent the wall’s depth. If, however, the city were a pyramid, the 144 cubits could represent either the height of the wall or its depth (since the wall would then be a separate structure from the city proper). Since John is not clear on this point, we may not pontificate on whether the number represents height or thickness.

A cubit was the distance from the elbow to the tip of the middle finger—and so approximately 18 inches or just over 45 centimetres (depending on the size of the man). Doing the math shows us that this wall was some 216 feet thick (or high) or some 65 meters—enormous numbers for a wall. But again, we are not to take this literally. The number 144 is itself obviously significant since it is the product of 12x12, that is, 12 squared. For the significance of the number 12, see the discussion on Revelation 21:16. Note too that in Revelation 7:4, Revelation 14:1, and Revelation 14:3, the number 144 (together with 1000) symbolized the totality or fullness or completeness of God’s people. That would give us the significance of the measurement of the wall; it ensures complete protection, for every last one of God’s chosen ones. The New Jerusalem is a place of perfect safety.