Sorry to disappoint you, Spencer, but your Church Pop website fails to deliver on its promise to explain the significance of December 25.
First, they believed that Jesus was crucified on March 25th (given when Passover normally falls), and there was a tradition that Jesus died the same day he first entered the world (his conception). Nine month later from March 25th is December 25th.
On this first point, the writer is correct about the generalized belief in the ancient world that great people lived an exact number of years, dying on the anniversary of their conception. It may even be true that this is the real reason why we celebrate Christmas on December 25. But, of course, it is of no help at all in establishing the historical date on which Jesus was born.
Second, and most importantly, Scripture provides strong evidence that December 25th, or a date near that, is when Jesus was born.
The Gospel of Luke tells us the angel Gabriel revealed to Zechariah that his wife Elizabeth would conceive John the Baptist while Zechariah was performing his priestly duties on the Day of Atonement, also known as Yom Kippur. That Jewish holy day always falls in late September or early October.
This second point is plain wrong. Luke’s Gospel does not say that Zechariah was performing his priestly duties ”on the Day of Atonement, also known as Yom Kippur.” The date isn’t mentioned at all.
All male descendants of Aaron were priests, entitled to officiate at the Temple sacrifices. They were divided into twenty-four groups, each of which served twice a year for a week at a time. Zechariah’s encounter with the angel Gabriel could have happened on any day of the year. We are not told the date. Luke says nothing about the time of year.