“Abbot Sugers theory of light . . . argued that man could come to a closer understanding of the light of God through the light of material objects in the physical world. This accounts for Sugers interest in magnificent liturgical vessels of gold and silver and also for the extraordinary set of stained-glass windows with which he adorned the radiating chapels of the chevert of St. Denis. He understood that stained glass had three basic properties: it was a bearer of holy images, an intrinsically rich material resembling precious stones, and a mystery, because it glowed without fire.”

—Robert Branner, from Gothic Architecture, 1965.