Ancient Romans celebrated Saturnalia, a wild weeklong unrestrained party. Here in America various Pueblo groups make elaborate preparations and perform sacred rites that relate to the reversal of migration of the Sun so that life might continue. When we get down to fundamentals, the reason people in the Northern Hemisphere have always felt the need for additional light in what we now call December is the fact that solar light has waned. With the Sun moving lower in the sky, each day becomes shorter and dimmer. What light does flow down is noticeably weaker, hitting our part of the world from a lower angle, becoming diminished and spread out over larger areas.
Weather responds, and all life feels the change.
Many plants lose their leaves or wither and die. Some creatures burrow into holes or find shelter deep inside caves to wait out the colder months. Humankind seeks solace in numbers. We huddle together around our hearths in comradeship, song and prayer, feeling each other's warmth and love more intimately and intensely than we do at other times of year. We tend to feel greater need for each other now than at times when abundant solar energy comes down from heaven.