This date has been the separation point of mankind's time on earth, with B.C. designating the era before Christ, and A.D., anno domino, in the Year of the Lord, the years after. And how stands Christianity today?
"Christianity is in danger off being wiped out in its biblical heartlands," says the British think tank Civitas.
In Iraq, Syria, Egypt, Ethiopia and Nigeria, Christians face persecution and pogroms. In Saudi Arabia and Afghanistan, conversion is a capital offense. In a century, two-thirds of all the Christians have vanished from the Islamic world.
In China, Christianity is seen as a subversive ideology of the West to undermine the regime.
In Europe, a century ago, British and German soldiers came out of the trenches to meet in no-man's land to sing Christmas carols and exchange gifts. It did not happen in 1915, or ever again.
In the century since, all the Western empires have vanished. All of their armies and navies have melted away. All have lost their Christian faith. All have seen their birthrates plummet. All their nations are aging, shrinking and dying, and all are witnessing invasions from formerly subject peoples and lands.
In America, too, the decline of Christianity proceeds.
While conservatives believe that culture determines politics, liberals understand politics can change culture.
The systematic purging of Christian teachings and symbols from our public schools and public square has produced a growing population -- 20 percent of the nation, 30 percent of the young -- who answer "none" when asked about their religious beliefs and affiliations.
In the lead essay in the Book Review of Sunday's New York Times, Paul Elie writes of our "post-Christian" fiction, where writers with "Christian convictions" like Walker Percy and Flannery O'Connor are a lost tribe.
"Where has the novel of belief gone?" he asks.
Americans understand why Mao's atheist heirs who have lost their Marxist-Leninist faith and militants Islamists fear and detest the rival belief system of Christianity. But do they understand the animus that lies behind the assault on their faith here at home?
In a recent issue of New Oxford Review, Andrew Seddon ("The New Atheism: All the Rage") describes a "Reason Rally" in Washington, D.C., a "coming out" event sponsored by atheist groups. Among the speakers was Oxford biologist Richard Dawkins, author of "The God Delusion," who claims that "faith is an evil precisely because it requires no justification and brooks no argument."
Christians have been infected by a "God virus," says Dawkins. They are no longer rational beings. Atheists should treat them with derisory contempt. "Mock Them!" Dawkins shouted. "Ridicule them! In public!"
In "The End of Faith," atheist Sam Harris wrote that "some propositions are so dangerous that it may even be ethical to kill people."
"Since the New Atheists believe that religion is evil," notes Seddon, "that it 'poisons everything,' in (Christopher) Hitchens' words -- it doesn't take much effort to see that Harris is referring to religions and the people who follow them."
Now since atheists are still badly outnumbered in America and less well-armed than the God-and-Country boys, and atheists believe this is the only life they have, atheist suggestions to "kill people" of Christian belief is probably a threat Christians need not take too seriously.
With reference to Dawkins' view that the Christian faith "requires no justification and brooks no argument," Seddon makes a salient point.
While undeniable that Christianity entails a belief in the supernatural, the miraculous -- God became man that first Christmas, Christ raised people from the dead, rose himself on the first Easter Sunday and ascended into heaven 40 days later -- consider what atheists believe.
They believe that something came out of nothing, that reason came from irrationality, that a complex universe and natural order came out of randomness and chaos, that consciousness came from non-consciousness and that life emerged from non-life.
This is a bridge too far for the Christian for whom faith and reason tell him that for all of this to have been created from nothing is absurd; it presupposes a Creator.
Atheists believe, Seddon writes, that "a multiverse (for which there is no experimental or observational evidence) containing an inconceivably large number of universes spontaneously created itself."
Yet, Hitchens insists, "our belief is not a belief."
Nonsense. Atheism requires a belief in the unbelievable.
Christians believe Christ could raise people from the dead because he is God. That is faith. Atheists believe life came out of non-life. That, too, is faith. They believe in what their god, science, cannot demonstrate, replicate or prove. They believe in miracles but cannot identify, produce or describe the miracle worker.
At Christmas, pray for Hitchens, Harris, Dawkins and the other lost souls at that Reason Rally.