Christmas has come and gone, but the subject will not go away. One of the main objections that we faced this year was the growing contention that the whole thing is of pagan origin, including the date set for it. This false premise has gained strength the last 30-40 years only, and has brought division and confusion into the Body of Messiah (which helps to discern the source of the trouble), and is a terrible witness to those still seeking the Lord of Glory, while seeing His ‘church’ scattered and accusing the brethren. The deligitimazation of the time of the Lord’s birth and its celebration is akin to the relentless and baseless efforts to deligitimize the existence of the State of Israel.
The ‘timeline’ which I have been working on for close to 20 years uses only Scripture to show that the birth of the Lord and its timing is not of pagan origin, but from God Himself. (There are Hebrew and Jewish roots to the historic celebration.)
https://streamsinthenegev.com/school-of-fish/conception-and-birth-of-john-the-baptiser-and-jesus-the-messiah/
Both Jewish believers and Gentile believers in Jesus/Yeshua are called outside their camps and systems to come together around the Throne of God. For those who would still be uncertain about the dating, there needs to be at least a softening of the condemnation against those who think that there is a valid reason for the historic remembrance and celebration from generation to generation, which keeps before the whole world — and to those within the household of faith — a testimony of this mighty act of God: that Messiah the Lord has indeed come, and was born in Israel.
From a Gentile side of how the date came to be set (and I do not submit to everything that is spoken about it), there is an thesis which I found some days after this past Christmas which gives evidence of how the time was set and the arguments for it; and it was done with a concern to be true to the new faith in those early years and to avoid the paganism from which they had come out. You can read it
here:
http://www.biblicalblueprints.org/pamphlets/december-25-in-jewish-style-volume-1/