My theory about solstice holidays is that people need to be cheered up and reminded that the long dark nights are over and the days will start getting longer. It doesn't really matter how you couch it in theology, lights are part of the magic somehow. Hannukah has the menorah. Christians have Christmas lights. The cult of Mithra believed the sun was born on December 25. The Hindu calendar begins on the winter solstice. Romans believed the happier times in the past were when there was no winter, so they celebrated Saturnalia, when the length of the day reverses and starts getting longer.