This is a Christmas season shadowed by sorrow. We know, of course, that human beings, even small ones, sometimes die in horrible, unfair ways. But all the horror and unfairness seemed to arrive at once in Newtown, where some parents wake on Christmas Day, if they slept at all, to mourn their absent children.

These events brought to mind a sermon by William Sloane Coffin, delivered 10 days after his son Alex was killed in a car accident. "When parents die," he said, "they take with them a large portion of the past. But when children die, they take away the future as well. That is what makes the valley of the shadow of death seem so incredibly dark and unending. In a prideful way it would be easier to walk the valley alone, nobly, head high, instead of – as we must – marching as the latest recruit in the world's army of the bereaved."

This army is easy enough to join. All of us build imaginary worlds of security that can be smashed in a moment by a drunken driver, a cancer diagnosis or an unnoticed patch of ice on the road. The death of a child may be the worst of our fears. But many of us find tragedy of some sort, with a little patience. It is the sad reality of grief: each loss infinite but not unique. And each loss sharpened during the holidays. A dark thought in a season of light.

There are no easy philosophical or theological explanations for unnatural death – no greater, cosmic good that neatly justifies unfair suffering. And those who try to find God's will in an earthquake, a cancer ward or a mass killing are engaged in a particularly cruel and arrogant exercise. Coffin would have none of it:

"Nothing so infuriates me as the incapacity of seemingly intelligent people to get it through their heads that God doesn't go around this world with his fingers on triggers, his fists around knives, his hands on steering wheels. … The one thing that should never be said when someone dies is 'It is the will of God.' Never do we know enough to say that. My own consolation lies in knowing that it was not the will of God that Alex die; that when the waves closed over the sinking car, God's heart was the first of all our hearts to break."

Death is not the expression of a just moral order but its violation. And the proper response is not explanation but friendship. "Immediately after such tragedy," said Coffin, "people must come to your rescue, people who only want to hold your hand, not to quote anybody or even say anything, people who simply bring food and flowers – the basics of beauty and life – people who sign letters simply, "Your brokenhearted sister."

Grief is particularly difficult at Christmas, as the best memories can be the hardest ones. But the hope of Christmas is broad enough for joy and sorrow.

The strangeness and scandal of the season get easily lost in its familiar rituals. In Christian belief, the boundless, timeless God became, in J.B. Phillips' phrase, one of those "crawling creatures of that floating ball."

From the beginning, many of the reasonable and pious found the whole idea to be nonsensical or blasphemous. But it is the central tenet of an enduring faith. Instead of setting out a philosophy to interpret the human drama, God joined it. He became "God with us" – a God with a face. In the process, he both shared and dignified ordinary human life, with all its delight, boredom and suffering. The Christmas story revels in this blasphemous elevation of the ordinary – a birth in second-rate accommodations under a cloud of illegitimacy.

And the story is also shadowed by sorrow. In one of the odder moments of the narrative, a random stranger at the Jerusalem Temple predicts a mother's grief. "A sword," Simeon tells Mary, "shall pierce through your own soul also." As it did. As it has for many mothers and fathers who have followed.

The point of Christmas is not a sentimental optimism about the human condition or even a teaching about the will of God. It is an assertion that God came to our rescue, and holds our hand, and becomes, at the worst moments, our brokenhearted brother. It is preposterous, unless it is true. And then it would be everything.

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