The Church does not teach that intercourse within marriage defiles the body. In Christian marriage such physical union is a holy thing. That quote expressing Mary’s perpetual virginity used a poor choice of words. Even though a marriage is consummated on the marriage bed, it is indeed valid the moment the vows have been spoken at the altar. The vows of religious life comprise an act of worship that direct the person to God in a more immediate way than do the vows of marriage. The process is considered higher because of its greater proximity to God. But the goals of both religious life and marriage are the same: union with God for all eternity. I encourage you to get the book Good News About Sex and Marriage by Christopher West (available through shop.catholic.com).