Here's a great post on Christmas preaching. Three points Barth emphasized about Christmas.
I'll summarize them in my own way, but read the original:
1) The inclusion of Bethlehem, Caesar Augustus, and Quirinius in the Christmas narrative reminds us that this not a myth, a legend, or fairy tale, nor even a morality tale of “peace and goodwill to all men.
We don't preach Christmas spirit but concrete fact, in the town of David a Saviour is born. We must embrace the scandal of particularity.
2) Not only is Christmas a mystery of God with us, it is a miracle of God with us.
This is the in-breaking of God into the world. A surprising and earth-shattering personal presence.
3) “The message of Christmas already includes within itself the message of Good Friday.” (CD II/2, 122.)
The crib and the cross are cut from the same piece of wood.
Read the whole thing here.