Analysis of information sources in references of the Wikipedia article "예수의 강탄" in Korean language version.
In the year 567 the church council of Tours called the 13 days between December 25 and January 6 a festival season. Up until that time the only other joyful church season was the 50 days between Easter Sunday and Pentecost.
This arrangement became an administrative problem for the Roman Empire as it tried to coordinate the solar Julian calendar with the lunar calendars of its provinces in the east. While the Romans could roughly match the months in the two systems, the four cardinal points of the solar year—the two equinoxes and solstices—still fell on different dates. By the time of the first century, the calendar date of the winter solstice in Egypt and Palestine was eleven to twelve days later than the date in Rome. As a result the Incarnation came to be celebrated on different days in different parts of the Empire. The Western Church, in its desire to be universal, eventually took them both—one became Christmas, one Epiphany—with a resulting twelve days in between. Over time this hiatus became invested with specific Christian meaning. The Church gradually filled these days with saints, some connected to the birth narratives in Gospels (Holy Innocents' Day, December 28, in honor of the infants slaughtered by Herod; St. John the Evangelist, "the Beloved," December 27; St. Stephen, the first Christian martyr, December 26; the Holy Family, December 31; the Virgin Mary, January 1). In 567, the Council of Tours declared the twelve days between Christmas and Epiphany to become one unified festal cycle.
The Council of Tours (567) decreed the 12 days from Christmas to Epiphany to be sacred and especially joyous, thus setting the stage for the celebration of the Lord's birth not only in a liturgical setting but in the hearts of all Christians.
Christmas in Sweden starts with Advent, which is the await for the arrival of Jesus. The symbol for it is the Advent candlestick with four candles in it, and we light one more candle for each of the four Sundays before Christmas. Most people start putting up the Christmas decorations on the first of Advent.
Around early December, an unusual kind of pilgrim starts to take the Prayag Raj from Delhi to Allahabad: the devout worshipper of the Allahabadi Christmas cake. This is no elegant western pudding – it is redolent with desi ghee, petha, ginger, nutmeg, javitri, saunf, cinnamon, something called cake ka jeera and marmalades from Loknath ki Galli. All this is browned to perfection at a bakery that has acquired cult status – Bushy's on Kanpur Road. The ancient city has had a great baking tradition. It could be because Allahabad has a sizeable population of Christians.
The Second Council of Tours (can. xi, xvii) proclaims, in 566 or 567, the sanctity of the "twelve days" from Christmas to Epiphany, and the duty of Advent fast; that of Agde (506), in canons 63–64, orders a universal communion, and that of Braga (563) forbids fasting on Christmas Day. Popular merry-making, however, so increased that the "Laws of King Cnut", fabricated c. 1110, order a fast from Christmas to Epiphany.
The Council of Tours (567) decreed the 12 days from Christmas to Epiphany to be sacred and especially joyous, thus setting the stage for the celebration of the Lord's birth not only in a liturgical setting but in the hearts of all Christians.