The city is the perfected state of consciousness in a person, and its being foursquare, equal in every direction, is the balance of a mind in which no faculty overpowers another. Length, breadth, and height are the same because the higher self, once whole, is symmetrical, the 4 sides answering the 4 elements and functions brought into agreement inside the one body. The number 12 is the number of the completed inner order, the full circle of the faculties, and 12000 is that completeness multiplied and confirmed.
Measuring the city with the reed is the exact weighing of that inner balance. A person arrives at this city not by travel but by bringing every part of the self into equal proportion until the whole stands square.
City: the finished, perfected state of consciousness a person becomes when the whole self is unified
Reed: the measuring rod of exact spiritual proportion, weighing the balance of the inner faculties
12000 furlongs: the number 12 of complete inner order, multiplied to confirm the fullness of the awakened self