Why is Christmas “the most unsentimental, realistic way of looking at life”? 
 
The Bible doesn’t say “from the world a light has dawned” but “upon the world a light has dawned.” The point is that the world is a dark place that needs salvation to come from outside of it. This means the end of cheery statements like, “If we all pull together, we can make the world a better place.” No, we can’t. We don’t have what it takes. This is a clear-eyed, realistic approach to our problems. It’s not rah-rah optimism. Yet it’s not pessimistic either, because there is hope, and a certainty that God will eventually destroy all evil.
 
Neither the god of moralism nor the god of relativism would have bothered with Christmas, you observe. Why not?
 
Moralism is essentially the idea that you can save yourself through your good works. And this makes Christmas unnecessary. Why would God need to become human in order to live and die in our place if we can fulfill the requirements of righteousness ourselves? Relativism is essentially the idea that no one is really “lost,” that everyone should live by their own lights and determine right and wrong for themselves. The “all-accepting god of love” many modern people believe in would never have bothered with the incarnation. Such a god would have found it completely unnecessary.
 
What can we learn about the difference between closed-minded doubt and open-minded doubt from contrasting Zechariah and Mary in Luke 1?
 
There’s a kind of doubt that really is seeking more information—that “wants” to believe if it’s possible. There’s also a kind of doubt that really is looking for a way out, that doesn’t want to believe or submit, that’s looking for a way to keep control of one’s own life.
 
This is a wonderfully nuanced approach to doubt. The Bible doesn’t view doubts as always rebellious, nor does it encourage people to live in doubt perpetually. That’s why we’re told to “be merciful to those who doubt” (Jude 1:22).