“We don’t divide time using Jesus’ birth. We divide it using a convention begun by a forgotten monk who made a mistake.”
It’s close enough for government work.
Well that is an article of faith for you.
Close enough to what? How would you know when it was?
There are arguments that Jesus was not born on 25 December, but his birth day was moved there for political reasons (shepards would not be in their fields by night that time of the year) to coincide with the Saturnalia, Mithra and Sol Invictus (winter solstice in the time of Romans).