Abbot Sugar's ambition was nothing less than to build the kingdom of God on earth, and in some measure he succeeded. Working in stone and glass with the best craftsmen of his day, Sugar undertook the restoration of the Abbey of Saint-Denis outside Paris, which became the prototype of the great gothic cathedrals of the 12th and 13th centuries. Through the use of heavy stone buttresses on the building's exterior, the interior walls could be raised on slender columns to unprecedented heights. To enter such a space was to feel simultaneously dwarfed and enlarged by a sense of God's grandeur. But it was not scale alone that Sugar was striving to achieve. Because the weight of the structure was borne by buttresses rather than by exterior walls, he was able to install large stained-glass windows between the support columns to illuminate the sacred space within. The abbot was influenced by the writings of Dionysius the Pseudo-Areopagite, a fifth-century monk and neo-Platonist who believed that God manifested himself through light. For Sugar, the stained-glass windows in his church "kindle in us the desire to ascend from a world of mere shadows and images to the contemplation of the Divine Light itself."
Mystics have long favored light as a metaphor for God, and many have described experiences in which the world suddenly appears as translucent as Abbott Sugar's stained-glass windows. Perhaps the archetypal experience of this kind was the gospel account of the transfiguration, in which Jesus and three of his disciples ascended a tall mountain where "he was transfigured before them, and his face shone like the sun, and his garments became white as light." The Greek word for "transfigured" normally refers to alterations in form as well as in appearance, which suggests that the change was more than skin deep.
Mystics are drawn to light as a metaphor because it is both tangible and immaterial. The distinguishing feature of a stained-glass window is not glass and lead, after all, but the light that shines through it. And yet without these materials, the light would be invisible. As it is, the illuminated world that mystics describe remains glass and lead to those who see only by the light of the sun. Or they assume there must be another world more brightly lit than this one. Mystical experiences tend to be fleeting and solitary, which is why they transform individuals more readily than history. It is not really the world that is illuminated by God's light but the sacred space within oneself.