Disclaimer: I mean no disrespect to those who believe in the god of the Christian faith, just exploring what makes sense to me.
As someone whose understanding of human culture goes back longer than two thousand and twenty one years, I find the central idea surrounding Christianity to be that of new beginnings symbolized by the metaphor of a baby.
Nothing is born in a vacuum especially not a new religious tradition. For example, the Christian Bible incorporates the written books of the Jewish tradition.
Historically in northern parts of the globe, the winter solstice was the end of darkness and the beginning of light, but as cultures do, they incorporate and alter earlier traditions — sometimes by violence and force for reasons of power and wealth.
Many of the traditions associated with Christmas in the USA actually come from pre-Christian northern European countries and the celebration of more light. When you live in the north, you can have six hours of sunlight a day leading up to the Solstice so the hope of more light is a really big deal.
This idea of new beginnings is a monumental idea for human culture that has resulted in positive and negative changes over the last two plus millennium. Yet like most cultural changes, it continues to evolve and many people have incorporated the idea of new beginnings into other religious traditions, or into psychology, medicine, and most of the new age practices that continue to evolve the idea.
The USA incorporates the idea of new beginnings into its more secular culture through social justice progress.
While I appreciate the invention of the idea, I believe in the sun and the moon, the wind and the 
stars, the oceans and the earth. They are magnificent, awe-inspiring miracles and all I need. If you prefer to live your life according to rules that are out-dated, have at it, but just understand, I will be living my life according to ideas from thousands of years ago and from the current year. The positive evolution of human culture goes forward. Just like you can’t keep your baby a baby forever.