What was the main purpose of medieval stained glass in churches?

The story behind the answer

Stained glass windows served as a visual catechism for largely illiterate medieval congregations. Panels narrated episodes from Scripture and saints’ lives in sequence, turning church walls into picture-books that clergy could reference during sermons. The imagery distilled doctrine into memorable scenes and symbols—lambs, keys, lilies—so worshippers could “read” theology through color and light.

Technically and theologically, the medium reinforced the message. Colored glass, tinted by metal oxides and joined by lead cames, flooded interiors with symbolic “new light” (lux nova), an idea championed by Abbot Suger in Gothic architecture. While windows certainly beautified churches, shaped atmosphere, and acknowledged donors, these were secondary to their catechetical role. Famous examples like Chartres’ rose windows pair dazzling craftsmanship with tightly structured biblical storytelling.