The Meaning of Stained glass
Stained glass appeared quite late, in christianity. Nowhere in the world, it is possible to see as many beautiful depictions as in the Sainte-Chapelle.
Divine light
Stained glass shows a deeper reality present in churches. A church itself is a representation of heaven on earth. In church, the Divine light shines through beautiful Biblical and saintly depictions and reaches you. This happens at two levels, firstly the visible level. The light literally, in the real world, shines through and reaches you. It also happens at the symbolic level, the light really does bring meaning. If there was no light from the outside, the windows would be dark and you could not decipher what was on the windows.
Modern change of glass
This is where the modern mind comes into play. The modern world cannot get rid enough quickly of these windows, to replace them with something inferior. These fall mainly into two categories: the chaotic or the abstract. While they do connect little to the meaning of Christianity, they enlighten some truths about the modern world.
The chaotic windows are a perfect representation of the modern world. Unconnected ideas integrated create a certain kind of primordial chaos, represented in the mind of modern man and represented in art.
The second is the mere abstract. The abstract has some hints of the traditional windows, but take away most of the rich symbolism. Sometimes, there is no symbolism at all. But even when there is no meaning meant, this still means something. It is the slow seeping away of the deep connection to the biblical narrative.
Art reflects the mind of a society. If the art is chaotic, the minds of the people are chaotic. If the art is ordered, the society is well ordered. Ideas are connected to their material manifestation and modern art has revealed its true intentions, to rip apart traditions. The only way to say no to this, is to not get caught up into the torrent of meaningless words attributed some random object. If a child is not fooled, so should you also not be.
Beauty is meaning. Beauty is Truth. Beauty is Goodness.