A careful analysis of Scripture, however, clearly indicates that December 25 couldn't be the date for Christ's birth. Here are two primary reasons:
First, we know that shepherds were in the fields watching their flocks at the time of Jesus' birth (Luke 2:7-8 Luke 2:7-8  And she brought forth her firstborn son, and wrapped him in swaddling clothes, and laid him in a manger; because there was no room for them in the inn.
 And there were in the same country shepherds abiding in the field, keeping watch over their flock by night.
American King James Version×). Shepherds were not in the fields during December. According to Celebrations: The Complete Book of American Holidays, Luke's account "suggests that Jesus may have been born in summer or early fall. Since December is cold and rainy in Judea, it is likely the shepherds would have sought shelter for their flocks at night" (p. 309).
Similarly, The Interpreter's One-Volume Commentary says this passage argues "against the birth [of Christ] occurring on Dec. 25 since the weather would not have permitted" shepherds watching over their flocks in the fields at night.
Second, Jesus' parents came to Bethlehem to register in a Roman census (Luke 2:1-4 Luke 2:1-4  And it came to pass in those days, that there went out a decree from Caesar Augustus that all the world should be taxed.
 (And this taxing was first made when Cyrenius was governor of Syria.)
 And all went to be taxed, every one into his own city.
 And Joseph also went up from Galilee, out of the city of Nazareth, into Judaea, to the city of David, which is called Bethlehem; (because he was of the house and lineage of David:)
American King James Version×). Such censuses were not taken in winter, when temperatures often dropped below freezing and roads were in poor condition. Taking a census under such conditions would have been self-defeating.
Given the difficulties and the desire to bring pagans into Christianity, "the important fact then which I have asked you to get clearly into your head is that the fixing of the date as December 25th was a compromise with paganism" (William Walsh, The Story of Santa Klaus, 1970, p. 62).
If Jesus Christ wasn't born on December 25, does the Bible indicate when He was born? The biblical accounts point to the fall of the year as the most likely time of Jesus' birth, based on the conception and birth of John the Baptist.
Since Elizabeth (John's mother) was in her sixth month of pregnancy when Jesus was conceived (Luke 1:24-36 Luke 1:24-36  And after those days his wife Elisabeth conceived, and hid herself five months, saying,
 Thus has the Lord dealt with me in the days wherein he looked on me, to take away my reproach among men.
 And in the sixth month the angel Gabriel was sent from God to a city of Galilee, named Nazareth,
 To a virgin espoused to a man whose name was Joseph, of the house of David; and the virgin's name was Mary.
 And the angel came in to her, and said, Hail, you that are highly favored, the Lord is with you: blessed are you among women.
 And when she saw him, she was troubled at his saying, and cast in her mind what manner of salutation this should be.
 And the angel said to her, Fear not, Mary: for you have found favor with God.
 And, behold, you shall conceive in your womb, and bring forth a son, and shall call his name JESUS.
 He shall be great, and shall be called the Son of the Highest: and the Lord God shall give to him the throne of his father David:
 And he shall reign over the house of Jacob for ever; and of his kingdom there shall be no end.
 Then said Mary to the angel, How shall this be, seeing I know not a man?
 And the angel answered and said to her, The Holy Ghost shall come on you, and the power of the Highest shall overshadow you: therefore also that holy thing which shall be born of you shall be called the Son of God.
 And, behold, your cousin Elisabeth, she has also conceived a son in her old age: and this is the sixth month with her, who was called barren.
American King James Version×), we can determine the approximate time of year Jesus was born if we know when John was born. John's father, Zacharias, was a priest serving in the Jerusalem temple during the course of Abijah (Luke 1:5 Luke 1:5THERE was in the days of Herod, the king of Judaea, a certain priest named Zacharias, of the course of Abia: and his wife was of the daughters of Aaron, and her name was Elisabeth.
American King James Version×). Historical calculations indicate this course of service corresponded to June 13-19 in that year (The Companion Bible, 1974, Appendix 179, p. 200).
It was during this time of temple service that Zacharias learned that he and his wife, Elizabeth, would have a child (Luke 1:8-13 Luke 1:8-13  And it came to pass, that while he executed the priest's office before God in the order of his course,
 According to the custom of the priest's office, his lot was to burn incense when he went into the temple of the Lord.
 And the whole multitude of the people were praying without at the time of incense.
 And there appeared to him an angel of the Lord standing on the right side of the altar of incense.
 And when Zacharias saw him, he was troubled, and fear fell on him.
 But the angel said to him, Fear not, Zacharias: for your prayer is heard; and your wife Elisabeth shall bear you a son, and you shall call his name John.
American King James Version×). After he completed his service and traveled home, Elizabeth conceived (Luke 1:23-24 Luke 1:23-24  And it came to pass, that, as soon as the days of his ministration were accomplished, he departed to his own house.  And after those days his wife Elisabeth conceived, and hid herself five months, saying,
American King James Version×). Assuming John's conception took place near the end of June, adding nine months brings us to the end of March as the most likely time for John's birth. Adding another six months (the difference in ages between John and Jesus (Luke 1:35-36 Luke 1:35-36  And the angel answered and said to her, The Holy Ghost shall come on you, and the power of the Highest shall overshadow you: therefore also that holy thing which shall be born of you shall be called the Son of God.  And, behold, your cousin Elisabeth, she has also conceived a son in her old age: and this is the sixth month with her, who was called barren.
American King James Version×)) brings us to the end of September as the likely time of Jesus' birth.
Although it is difficult to determine the first time anyone celebrated December 25 as Christmas Day, historians are in general agreement that it was sometime during the fourth century. This is an amazingly late date. Christmas was not observed in Rome, the capital of the Roman Empire, until about 300 years after Christ's death. Its origins cannot be traced back to either the teachings or practices of the earliest Christians.
To learn more about the origins of Christmas, read the following online Bible study resources:
Bible Study Aid Booklet: Holidays or Holy Days: Does It Matter Which Days We Observe?