It is unknown exactly when or why December 25 was originally associated with Jesus' birth; the New Testament does not name a specific date. [13] Sextus Julius Africanus popularized the idea that Jesus was born on December 25 in his Chronographiai, a reference book for Christians written in 221 AD.[13] This date is nine months after the traditional date of the Incarnation (March 25), now celebrated as the Feast of the Annunciation.[17] March 25 was also considered to be the date of the vernal equinox and therefore the creation of Adam.[17] Early Christians believed March 25 was also the date Jesus was crucified.[17] The Christian idea that Jesus was conceived on the same date that he died on the cross is consistent with a Jewish belief that a prophet lived an integral number of years.[17]

The identification of the birthdate of Jesus did not at first inspire feasting or celebration. Tertullian does not mention it as a major feast day in the Church of Roman Africa. In 245, the theologian Origen denounced the idea of celebrating Jesus' birthday "as if he were a king pharaoh." He contended that only sinners, not saints, celebrated their birthdays.[7] His criticism may be inspired by his contact with Egypt as Origen was born in Alexandria.

The earliest reference to the celebration of Christmas is in the Calendar of Filocalus, an illuminated manuscript compiled in Rome in 354.[3][18] In the east, meanwhile, Christians celebrated the birth of Jesus as part of Epiphany (January 6), although this festival focused on the baptism of Jesus.[19]
Christmas was promoted in the east as part of the revival of Nicene Christianity following the death of the pro-Arian Emperor Valens at the Battle of Adrianople in 378. It was introduced to Constantinople in 379, to Antioch in about 380, and to Alexandria in about 430. Christmas was especially controversial in 4th century Constantinople, being the "fortress of Arianism," as Edward Gibbon described it. The feast disappeared after Gregory of Nazianzus resigned as bishop in 381, although it was reintroduced by Saint John Chrysostom in about 400.[3]

Middle Ages

Adoration of the Magi by Don Lorenzo Monaco (1422).
In the Early Middle Ages, Christmas Day was overshadowed by Epiphany, which in the west focused on the visit of the magi. But the Medieval calendar was dominated by Christmas-related holidays. The forty days before Christmas became the "forty days of St. Martin" (which began on November 11, the feast of St. Martin of Tours), now known as Advent.[20] In Italy, former Saturnalian traditions were attached to Advent.[20] Around the 12th century, these traditions transferred again to the Twelve Days of Christmas (December 26 - January 6).[20] The evening of January 5 was called Twelfth Night, a festival later celebrated in the play of that name by William Shakespeare. The fortieth day after Christmas was Candlemas.
The prominence of Christmas Day increased gradually after Charlemagne was crowned on Christmas Day in 800. King William I of England was crowned on Christmas Day 1066.
By the High Middle Ages, the holiday had become so prominent that chroniclers routinely noted where various magnates celebrated Christmas. King Richard II of England hosted a Christmas feast in 1377 at which twenty-eight oxen and three hundred sheep were eaten.[20] The Yule boar was a common feature of medieval Christmas feasts. Caroling also became popular, and was originally a group of dancers who sang. The group was composed of a lead singer and a ring of dancers that provided the chorus. Various writers of the time condemned caroling as lewd, indicating that the unruly traditions of Saturnalia and Yule may have continued in this form.[20] "Misrule" — drunkenness, promiscuity, gambling — was also an important aspect of the festival. In England, gifts were exchanged on New Year's Day, and there was special Christmas ale.[20]
Often the "misrule" got quite out of hand. According to the History Channel's documentary, Christmas Unwrapped: The History of Christmas, there was even a Christmas custom pre-dating trick-or-treat, in which revelers would knock at a door and demand the best portion of their host's food and ale, with "severe consequences" if he did not agree.

Excerpt from Josiah King's The Examination and Tryal of Father Christmas (1686), published shortly after Christmas was reinstated as a holy day in England.

The Reformation and the 1800s
During the Reformation, Protestants condemned Christmas celebration as "trappings of popery" and the "rags of the Beast". The Catholic Church responded by promoting the festival in an even more religiously oriented form. Following the Parliamentary victory over King Charles I during the English Civil War, England's Puritan rulers banned Christmas, in 1647. Pro-Christmas rioting broke out in several cities, and for several weeks Canterbury was controlled by the rioters, who decorated doorways with holly and shouted royalist slogans.[21] The Restoration of 1660 ended the ban, but most of the Anglican clergy still disapproved of Christmas celebrations, using Protestant arguments.

In Colonial America, the Puritans of New England disapproved of Christmas; its celebration was outlawed in Boston from 1659 to 1681. At the same time, residents of Virginia and New York celebrated the holiday freely. Christmas fell out of favor in the United States after the American Revolution, when it was considered an English custom.

By the 1820s, sectarian tension in England had eased and British writers began to worry that Christmas was dying out. They imagined Tudor Christmas as a time of heartfelt celebration, and efforts were made to revive the holiday. Charles Dickens' book A Christmas Carol, published in 1843, played a major role in reinventing Christmas as a holiday emphasizing family, goodwill, and compassion over communal celebration and hedonistic excess.[22]

During the early part of the 19th century, interest in Christmas in America was revived by several short stories by Washington Irving in The Sketch Book of Geoffrey Crayon and "Old Christmas", which depicted harmonious warm-hearted holiday traditions Irving claimed to have observed in England. Although some argue that Irving invented the traditions he describes, they were imitated by his American readers.[23] The numerous German immigrants and the homecomings following the American Civil War helped promote the holiday by bringing with them continental European Christmas traditions still upheld in Catholic and Lutheran countries on the continent. Christmas was declared a U.S. federal holiday in 1870.

source: Wikipedia