THE BRIEF AND POTENT PRAYERS OF THIS WEEK of the Advent season so beautifully weave together all the many themes of Advent.  They have been used at least since the seventh century in [Western Christian] monasteries, which are among the few remaining communities still singing them to mark the week beginning December 17 as a special time in the Advent season. Some Benedictine hospitals keep this tradition as well; only in the pediatric ward will you see