I'm guessing here, but here's a go: Symbolically would mean that it represents something to do with the human condition. In the case, I would imagine, he means

I'm guessing here, but here's a go: Symbolically would mean that it represents something to do with the human condition. In the case, I would imagine, he means that the design of cathedrals and great music both tap into some kind of perfect or balanced thing in humans. Such a thing is something to aim for, or towards. Its how we cant write a recipe to how to write great (not just good, but the real stuff that makes your hair stand on end) music - and that sense of awe we feel in a cathedral. And both are man made and not a natural beauty. He has also talked about the cross formation of most churches, but I don't think that quote was about that.