The actual birthday of Jesus Christ is not known and it is good. If that day were known, certain religious people would have overly hallowed that day into idolatry. Since that day is not known, why do Christians celebrate the birthday of Jesus on 25th December?
Through the writings of a man called Jacob Bar-Salibi, a 12th-century Syrian bishop, we learn that during his time, there was this belief that the early Christians chose 25th December to celebrate Christmas because the Pagan Romans were celebrating the birthday of the sun god on the same 25th December. During the celebration of this pagan festival, the Christians were enticed to participate in it. For this reason, the leaders of the church thought wisely to fix the celebration of the birth of Jesus on 25th December to deter the believers from committing idolatry by participating in the Pagan festival.
The festival of the birthday of the sun god was called Dies Natalis Solis Invicti (birthday of the Unconquered Sun). In AD 274, the Roman emperor Aurelian rejuvenated and instated the worship of the sun as a state religion on 25th December. Therefore, every 25th December is made a holiday for the celebration of the festival called Dies Natalis Solis Invicti, which consists of offering sacrifices, bonfires, feasting, gifting, and thirty chariot races to honor the sun god Sol Invictus, Prior to this festival, from 17th to 23rd December, there was another Roman festival called Saturnalia celebrated in honor of Saturn, their god of agriculture. The festival of the birth of the sun adds up to Saturnalia to make a long joyous season.
For many years up to this day, it has become a popular hypothesis that the early church chose December 25th to celebrate Christ’s birthday to appropriate the Roman winter solstice festival Dies Natalis Solis Invicti and that they did so to continue enjoying pagan festivals under the guise of commemorating the birth of Jesus.
However, the earliest records about Christmas say otherwise. Christmas was celebrated as early as 129 AD. Records have it that as far back as the second century AD Christians recognized 25th December as the proposed birthday of Jesus, a day fitting for the celebration of Christmas. According to a Roman historian Sextus Julius Africanus (AD 160 – AD 240) who lived in the second century, Jesus of Nazareth was conceived on 25th March and, since pregnancy lasts for nine months, was born on 25th December.
According to a five-volume book written by Africanus, the birth of Jesus on 25th December is supported by the opinion that Angel Gabriel announced the conception of John the Baptist to Zachariah during the observation of Yom Kippur, a festival that occurred in October. During this festival, the worshippers prayed outside the temple, not inside; and only the priest could enter the temple to perform the proper rituals. And since John was six months older than Jesus, Jesus was conceived in March of the following year and born on December 25th.
Since 2nd century believers had reasoned that Jesus was born on 25th December, it might have been that the celebration of Christmas started from there, probably, on a small scale before the emperor instituted Dies Natalis Solis Invicti in the 3rd century. That is why some scholars believe that Emperor Aurelian intentionally fixed the festival of the birthday of the sun on 25th December to give the day a pagan significance.
Christians started with 25th December before the pagans, history says so. It was 34 years after the death of Africanus that 25th December became a significant day for the pagan Romans. From 274 AD, on every 25th December, while Christians were celebrating the festival of the birth of the Savior Jesus Christ to the glory of God, the pagans were celebrating the festival of the birth of the unconquered sun to honor the sun god.
We should bear in mind that a day may be evil or holy to you depending on what you do on that day. On the same day, while one person is doing a holy deed, another person is committing a heinous sin; while one person is doing an act of worship to God, another person is rendering his to the devil. There is no general holy day.
Therefore the celebration of Christmas on the same day as the celebration of a pagan festival does not profane Christmas, or make it less spiritual, or idolatrous. Christmas, when celebrated in commemoration of the birth of Jesus is a holy festival and it is approved by God.