So Jesus was born in spring or late summer depending on who you ask. But Christmas was chosen to compete with Saturnalia or Solstice depending on who you ask.
Solstice is usually or always December 21st, how did Christmas end up 4 days off?
u/Gadarn answered this question several years ago: Why was Christmas placed on the 25th and not the 21st in accordance with most of the winter solstices?