The angel measured the city with his measuring stick: it was fifteen hundred miles long, and was as wide and as high as it was long. – Revelation 21:15

The Holy City symbolizes a psychological state of being whole, and the number attributed to it is fifteen. To be whole, an equal pair of opposites must coexist. There are seven rungs to Heaven, balanced by the seven rungs to Hell. Together, there are fourteen rungs; where they meet is the zero point, the fifteenth.