For centuries, Christian writers accepted that Christmas was the actual date on which Jesus was born.  John Chrysostom preached a sermon in Antioch c. 386 which established the date of Christmas as December 25 on the Julian calendar since the conception of Jesus (Luke 1:26) had been announced during the sixth month of Elisabeth's pregnancy with John the Baptist (Luke 1:10-13) as dated from the duties Zacharias performed on the Day of Atonement during the seventh month of the Hebrew calendar Ethanim or Tishri (Lev. 16:29, 1 Kings 8:2) which falls in September–October.

In the early 18th century, scholars began proposing alternative explanations. Isaac Newton argued that the date of Christmas was selected to correspond with the winter solstice, which the Romans called bruma and celebrated on December 25. In 1743, German Protestant Paul Ernst Jablonski argued Christmas was placed on December 25 to correspond with the Roman solar holiday Dies Natalis Solis Invicti and was therefore a "paganization" that debased the true church. In 1889, Louis Duchesne proposed that the date of Christmas was calculated as nine months after the Annunciation, the traditional date of the conception of Jesus, which itself was based on a traditional belief that he was conceived and crucified on the same date, 15 Nisan.

In the early 4th century, the church calendar contained Christmas on December 25 and other holidays placed on solar dates: "It is cosmic symbolism...which inspired the Church leadership in Rome to elect the winter solstice, December 25, as the birthday of Christ, and the summer solstice as that of John the Baptist, supplemented by the equinoxes as their respective dates of conception. While they were aware that pagans called this day the 'birthday' of Sol Invictus, this did not concern them and it did not play any role in their choice of date for Christmas," according to modern scholar S.E. Hijmans.  However, today, whether or not the birth date of Jesus is on December 25 is not considered to be an important issue among mainstream Christian denominations;rather, celebrating the coming of God into the world in the form of man to atone for the sins of humanity is considered to be the primary meaning of Christmas.

Eastern Orthodox national churches, including those of Russia, Georgia, Ukraine, Macedonia, Montenegro, Serbia and the Greek Patriarchate of Jerusalem mark feasts using the older Julian calendar. December 25 on the Julian calendar currently corresponds to January 7 on the internationally-used Gregorian calendar. However, other Orthodox Christians, such as the churches of Greece, Romania, Antioch, Alexandria, Albania, Finland and the Orthodox Church in America, among others, began using the Revised Julian calendar in the early 20th century, which corresponds exactly to the Gregorian calendar.

These Orthodox Churches celebrate Christmas on the same day as Western Christianity. Oriental Orthodox churches also use their own calendars, which are generally similar to the Julian calendar. The Armenian Apostolic Church celebrates the nativity in combination with the Feast of the Epiphany on January 6. Armenian churches customarily use the Gregorian calendar, but some use the Julian calendar and thus celebrate Christmas Day on January 19, and Christmas Eve on January 18 (according to the Gregorian calendar).

Commemorating Jesus' Birth

Christians celebrate the birth of Jesus to the Virgin Mary as a fulfillment of the Old Testament's Messianic prophecy.^[27] The Bible contains two accounts which describe the events surrounding Jesus' birth. Depending on one's perspective, these accounts either differ from each other or tell two versions of the same story. These biblical accounts are found in the Gospel of Matthew, namely Matthew 1:18, and the Gospel of Luke, specifically Luke 1:26 and 2:40. According to these accounts, Jesus was born to Mary, assisted by her husband Joseph, in the city of Bethlehem.

According to popular tradition, the birth took place in a stable, surrounded by farm animals, though neither the stable nor the animals are specifically mentioned in the Biblical accounts. However, a manger is mentioned in Luke 2:7, where it states, "She wrapped him in cloths and placed him in a manger, because there was no room for them in the inn." Early iconographic representations of the nativity placed the animals and manger within a cave (located, according to tradition, under the Church of the Nativity in Bethlehem). Shepherds from the fields surrounding Bethlehem were told of the birth by an angel, and were the first to see the child.

The Gospel of Matthew also describes a visit by several Magi, or astrologers, who bring gifts of gold, frankincense, and myrrh to the infant Jesus. The visitors were said to be following a mysterious star, commonly known as the Star of Bethlehem, believing it to announce the birth of a king of the Jews.^[33] The commemoration of this visit, the Feast of Epiphany celebrated on January 6, is the formal end of the Christmas season in some churches.

Christians celebrate Christmas in various ways. In addition to this day being one of the most important and popular for the attendance of church services, there are other devotions and popular traditions. In some Christian denominations, children re-enact the events of the Nativity with animals to portray the event with more realism or sing carols that reference the event. Some Christians also display a small re-creation of the Nativity, known as a Nativity scene or crèche, in their homes, using figurines to portray the key characters of the event. Prior to Christmas Day, the Eastern Orthodox Church practices the 40-day Nativity Fast in anticipation of the birth of Jesus, while much of Western Christianity celebrates four weeks of Advent. The final preparations for Christmas are made on Christmas Eve.

A long artistic tradition has grown of producing painted depictions of the nativity in art. Nativity scenes are traditionally set in a barn or stable and include Mary, Joseph, the child Jesus, angels, shepherds and the Three Wise Men: Balthazar, Melchior, and Caspar, who are said to have followed a star, known as the Star of Bethlehem, and arrived after his birth