Why December 25? In the old pre-Iulian calendar created by Eudoxus of Cnidus in the 6th Century BCE, the sun entered Capricorn (and the Winter Solstice occurred) on December 24, so the 25th was the day on which the light of the new year was born. The Eudoxan calendar is also the reason why the Day of Blood was March 24th... which was the Eudoxan Equinox.
So, whatever darkness may be in the world, the solution begins with us, and it begins today. Happy December 25th!