In The Book of Zechariah, two angels measure the city of God, attempting to define and bound it, but finding that the City will be so overflowing with multitudes that it shall be inhabited as a "town without walls." However, the LORD will be a "wall of fire" round about and a "glory in the midst of her." Though there are no walls limiting the Celestial City, the fire of the LORD both animates and restrains it, an outer flame with an inner, echoing glory, and God in the center and the circumference. The fire is of the creative rather than destructive variety; the same beatific flames which entwined around the Bush on Mount Horeb. The "glory" is the restored Presence of God which the anguished Ezekiel witnessed as it departed from the holy city.
In the City of God there are no external, literal walls of worldly boundary--only the fiery walls of Vision--of God's Glory as His Presence dwells within the limitless City. This reciprocal relationship of inner and outer fire must be reproduced within each of us in our dealings with the Divine.