The words in the Psalm set for tonight's mass, to "sing a new song to the Lord" because a Savior is born, sum up this gracious feast as well as any other of its memorable texts. We've heard them so often; we know them all by heart, and love them none the less for that. In like manner a solid month of Christmas carols on the air cannot rob us of their evocative magic or make us hear them as anything but beautiful.

Birthdays are, however, messy. The problem is that they keep adding up. For a short while we look forward to them. The 5-year-old will tell you to the month how close he is to 6. But when was the last time you heard someone say, "I'm forty-nine-and-a-half." No, the wretched things keep totaling, and most of us, like Shakespeare, "love not to have years told."

Christmas, however, doesn't look to our birthdays, but to the birth of the infant Christ, to the first time men and women could see and touch the incarnation, God made man. Each year with music, with lights, we reenact the birth of Christ, reaching in our carols for the songs of angels, and in our decorations for the light of God's presence.

Reenactment for those of us who live and work in universities is almost commonplace. Every year, quite outside of the order of generation, we renew ourselves with the freshman class that brings the drive and beauty of youth but also reenacts for us the days of our own launching as members of a learned and learning society. There is intellectual reenactment as we rediscover knots already untied, long roads already mapped, and glean from well-remembered ground new beauties, new colors, new joys. Reenactment is ours as we watch students wrestle with the same puzzles year in and year out as once we did. The faces, the voices, the years tend to blur, but the wrestle doesn't.

Another reenactment for universities is on new, not old, ground -- in research. We repeat our days as graduate students, pushing out across our terrain but always on the edge of it, always uncomfortable, always probing beyond our maps. Here we rediscover the excitement of discovery itself, what Housman called the tingling at the base of the spine that comes from getting it right, especially when no one else has got it right before us.

A deeper renewal comes outside of classroom and lab and lecture hall, as we talk to the young. For them we apply old truths to new problems, old salve to new wounds, and sometimes against the scriptures fill new skins with old wine. For faculty who are parents, the reenactment is doubly haunting, as in their students they see the puzzlements their own children have known or will know, along with the echo across shared decades of the pain and the clamor of growing up.

The reenactment we celebrate this night is different. It isn't echo or d,ej vu. We can make no claim to own this event, and for all our Christmases past we can make no claim to have sounded it. It changes as we do. This day recalls our joy and delight as children, when we missed the greatest gift but lost ourselves in the lesser ones, and were enchanted by the stable with its angels, animals and baby. Christmas also brings back to us a young adult's wrestle with faith and the works it calls for, all the complexity of fitting belief into the pulls and tugs of marriage and earning a living.

Later comes depth as we come to know ourselves mined by the motion of faith, the mature grasp that our belief works, even if its machinery is hidden from us. And finally when age makes it easy to own up to our limitations, caught between unbeing and being, we can slowly grow into hope. If old men ought to be explorers, what they must explore even through ways that are dark, cold and empty, is a deeper communion.

The coming of Christ into our lives is more than reenactment. As Christians we do not know the isolated moment with no before or after, but "a lifetime burning in every moment." We reenact tonight "the point of intersection of the timeless with time," the coming of the Lord God himself into our world, our community, our hearts. Increasingly we come to know that Christmas is an invitation to a lifetime's death in love: that the love returned to us is always greater than we give.