You have to experience it for yourself.
This is right up there with the Grand Canyon at sunset for being the most awe-inspiring place I've ever been. In fact, we wouldn't have stopped by there if I hadn't read a review on-line by a person who said it stood up to the cathedrals in Europe. Words simply cannot convey the beauty, artistry, and feeling of reverence in the Cathedral. You needn't be Catholic (I'm not) to be blown away by this. Just go.