The truth of the matter is that on Dec 25, Jesus was conceived in Mary by the overshadowing of the Holy Spirit as written in Luke 1:26-35. Nine months later, Jesus was born on Sept 29, during the feast of tabernacles, when the herds and shepherds would still be in the fields. This is all based on the date of the course of Abia that Zacharias served between June 13-19. After Zacharias' service he went home and impregnated Elisabeth according to the word of the angel of the Lord as written in Luke 1:11-17. The Lord was conceived on Dec 25, six months after Elisabeth became pregnant by Zacharias. Jesus indeed began living among men as he was conceived in Mary on Dec 25. His conception should be celebrated on Dec 25 as well as his birth on Sept 29. The whole first chapter of Luke explains the conception and birth of Jesus in connection with the conception of John the baptist.