December 25th is not actually the birthday of jesus, no where in the bible his birthday is stated..
Only his last day i.e nissan 14 is registered.. based on his age on his last day , he must have born in the month of September or October..
But definitely not in December..
Pagan festival is later announced as Christmas..
And fyi, Jesus wanted his followers to remember his death but he never mentioned about celebrating his birthday.. because he thought that His (death)Maranam is more important to be remembered than his (birth)Jananam..
But actually when u search history, all the festivals, whether it's Christmas or Ramzan or diwali ,
everything is celebrated for people's happiness and to share Love 

..