Why were medieval church builders interested in bringing more light into cathedrals?

Medieval church builders were driven by the theological belief that light is the most direct manifestation of God. This conviction inspired a concerted effort to transform the interiors of cathedrals into spaces filled with a mystical, supernatural diffusion of light.12

To achieve this, architects moved away from the heavy, thick-walled structures of the Romanesque period, which necessitated small windows. Through structural innovations—most notably the development of the ribbed vault, the pointed arch, and the flying buttress—masons were able to shift the weight of the ceiling to discrete piers. This relieved the vertical walls of their supportive function, allowing them to be built thinner and opened up with expansive stained-glass windows.31

This architectural evolution allowed for the creation of soaring, light-filled spaces where the masonry seemed to dissolve into glass, effectively turning the cathedral into a vessel for divine illumination.342