(These are my notes, not necessarily my exact words...)
1. What we believe: Mary, at the end of her life on earth, was taken up, body and soul, into heaven.
2. Notice the importance of the body. Our body is not just a shell we leave behind, but part of who we are; if we go to heaven, while there we will await the resurrection of our bodies. This is why some things are sinful--because our body is part of our salvation (or damnation).
3. Mary is the ark of the new covenant; the ark in the Old Testament held the tablets of the law and the manna, and it was precious and God punished those who dishonored it; how much more Mary, who held the Word made flesh and the Bread of Heaven! Thus God was not willing to have her body undergo corruption. This was gratitude from a grateful Son to his mother, along with being conceived without sin. It was important to God that she be adorned with grace and beauty; and we feel the same, for example, when we depict Mary in artwork; we don't show her in drab or work clothes!
What Mary was in the incarnation, our church is now: the ark of the new covenant! So it is appropriate that, within our means, we make our church beautiful, and many generations have done so. It is fitting that our worship of God not only be about "doing the minimum," but also be about beauty.
4. We do the same with our own lives: that we will be arks of the new covenant, bearing Christ in our lives. What Mary is, God wants us to be; where Mary is now, we are meant to be. The Sacraments are how we do that.
(Sorry, I simply don't recall how I ended this homily--there ends my notes...)