It is said by many history scholars that Jesus was not born in winter. And the Scriptures never tell us to celebrate his birth every year.
Scripture never says any kind of law or rule saying believers should either celebrate every year or must only celebrate on a kind of year. In many ways, it is a non-issue and something that is a matter of majoring on minors and minoring on majors when it becomes an obsession to examine churches that enjoy celebrating the concept of Christ's birth during the winter (and many of those same churches already agree he probably wasn't born during the Winter).
If one loves someone, they celebrate that person every day and every moment. If a husband comes home and brings a gift for his wife, it would be wrong for the wife to say "Well, it's not my birthday!!" when the reality is that love is simply being shown to the wife by a husband who feels she's worth celebrating often (not just designated days). It's the same for believers, be it Jew or Gentile, all around the world who celebrate the Birth of Messiah and what that means for humanity being redeemed/saved. IMHO, for the many people that fight over the issue with others in saying they can't celebrate, they dishonor Yeshua in the same way the apostles did when the woman came in, anointed his feet with perfume and washed them with her hair and the apostles were indignant.
In the period soon after Constantine when Romanism Christianity became the Royal religion. Many many new “Christians” did not know What monotheism was. A simply answer was:”You don’t know whom ‘God’ is? Never mind. ‘God’ is like our Roman God Jupiter (Zeus, Deus)!” 
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There were a lot of new Christians who came out of a polytheistic culture and understood pantheons...and thus, to hear of Christ and God the Father/Holy SPirit meant that there were 3 differing Gods. The body of believers did have a good system of handling that so that others would know that God is One and yet in 3 differing persons...one of the reasons why settling the debates about the Trinity were such a big deal in the early church since many were saying there could never be such a thing as a Trinity due to how they felt it was supporting the theology of Roman Pantheons---and others saying "God is One" who didn't believe in Yeshua and already felt he was blasphemous for his statements on being ONE with the Father and yet submitted to Him. T
rue biblical understandings of God the Father, Jesus Christ, and the Holy Spirit were corrupted in the third, fourth, and fifth centuries by Greek philosophy and pagan polytheism, which led to the development of the doctrines of the Trinity and the deity of Christ.
For the Jews apart of the early church/body of believers, it was a very tricky issue getting them to see the ways that following Yeshua didn't mean one was no longer Jewish in saying "God is One"----and for many,
Binitarian Monotheism and Jewish Binitarianism came to be a dominant view in the early church held that viewpoint. Dozens of Biblical scholars who are believers in Christ being Divine/God have said that for ages, if aware of what's said in church history. Michael Heiser (of Logos Bible Software used throughout the body of Christ) being one of the most recent
(as it concerns his thoughts on the ancient Judaic perspective of the Divine Council/Plurality within the Godhead)..and as said before, one can go to places such as
Yeshua & Worship /
here as well:
Even for those saying that they believe in Monotheism (unlike many of the new believers who struggled in the early church), some of the same issues remain today when understanding the Jewish concept of the Shema ("Hear O Israel, the Lord Our God, the Lord is One).
People often think in Western culture that something isn't "worship" due to them actively giving attention to it--like saying "I worship Satan" when living for themselves---but one can worship something without knowing it if/when their lifestyle lines up directly with something counter to Christ. That's why idolatry is often one of the most difficult sins to get rid of since many live in a world of dualism where they try to seperate elements that were never meant to be seperated.
One Messianic Jew, known as Alan Hirsh, tried to address it the best (IMHO) when it came to noting Dualism in the Christian world.....and life in general. For when people try to say things such as "this is sacred" or this is "secular" and don't see the Lord in all things, they tend to try to create categories where none exist...and tolerate behaviors that normally would not be acceptable because they treat certain areas of their lives as "seperate" from their walks with the Lord. For more, one can go online/look up the work entitled the following:
Alan Hirsch, in the book, the Forgotten Ways, offers the following reflection:
"Isn't it interesting that most churchgoers report a radical disconnect between the God that rules Sunday to the gods that rule Monday? How many of us live as if there were different gods for every sphere of life? A god for work, another for family, a different one when we are at the movies, or one for our politics. No wonder the average churchgoer can't seem to make sense of it all. All this results from a failure to respond truly to the One God. This failure can be addressed only by a discipleship that responds by offering all the disparate elements of our lives back to God, thus unifying our lives under his lordship" (97).
Polytheism doesn’t have a unfied God that controls all spheres. Each sphere has its own god. Most of those gods didn’t care much for human beings and it was often a dangerous life as people saw it since you always ran the risk of offending (one of the reasons for the Unknown God by those in Athens in Acts 17 ). If they were at the river, they'd act a certain way so as to entertain the river god/have favor and not be harmed....but when walking down a dirt path, they may've felt they needed to be different so as to not offend a nature god/spirit....and when home, they'd make sacrifices to another god for success. There was not consistency. Polytheism ruled the day of the New Testament. Into this context came the claim that ‘there is only one God and His name is Yahweh.’ This was a call to loyalty. As a result, all domains of our lives were told to come under submission to the one God (rather than being loyal to lots of gods). For worship is offering all of our world back to God and Biblical discipleship calls people towards a unification of our life to God.
Sadly, there are a myriad of ways people can end up living like de-facto polytheists and not really understand it. And it's something to remember today. Again, the original Hebrew context was polytheistic...one of the reasons the Lord often had to come to them/say that they needed to get rid of other gods and why they often seemed prone to think God (El Shaddai) was like the Cannanite god EL (who also allowed for other gods to serve him). To the early Hebrews, the message to them was, Hear O Israel, the Lord our God, the Lord is one; love the Lord your God with all your heart, soul, strength. (Deut 6.4-9). Torah relates all aspects of life to God – from the temple to what you do when your donkey falls into a pit. The early church proclaims ‘Jesus is Lord’ in the same way; the gods were different, but still many, as indeed they are today. They refused to keep the pantheon and the overlordship of Caesar...for Jesus is Lord. We have adopted Christocentric monotheism...so genuinely Messianic monotheism rejects separation of sacred from secular. Our task is to make all aspects of life sacred, and not to limit the presence of God to spooky religious zones. God is not only encountered in special places, requiring a priestly paraphernalia to mediate our experience of him. God, Church and World are three overlapping circles (not God and World separate with Church in the middle linking them!). Our task is to integrate all aspects of life under the lordship of Jesus – leave one out (eg apartheid, or work) and disaster follows. In Rwanda, ‘Christian’ served as a brand name, but not a commitment to a common Lord, which would have stopped Christians killing one another.
Anytime dualistic, while we may be confessing monotheists, we may end up practicing polytheists..for dualistic expressions of faith always lead to practical polytheism.
I'm with you, Contra, all this screaming about paganism is really silly. If a believer wants to have a christmas tree and decorations and presents on Dec. 25 in a celebration of Yeshua's birth - there is nothing wrong in this. What's wrong is using this designated time as a time to PARTEE without a thought to the holiness that is what brought it all about.
Who am I to judge how they choose to celebrate our Master? When all is said and done, it may be us who don't celebrate it that were wrong, and I sure don't want to stand beneath my own harsh judgment, that's for sure, 'cause we humans are great at passing judgment 
if we don't check ourselves constantly! Whew! may it never be! 
