Why is it called Christmas?
Ever wondered where Christmas got it's name? It comes from the combination of two words - "Christ's Mass," which was a special church service celebrating the birth of Jesus that started in the Catholic Church in the mid-fourth century. Masses are services where the Lord's Supper (Eucharist) is taken.
Etymological Origins of the word "Christmas"
The word "Christmas" derives from an Old English term that dates back to 1038: "Cristes Maesse." The term literally means "the mass of Christ," which is evidence of its Catholic roots. "Mass" comes from the Latin missa, and refers to the service of Eucharist, or the Lord's Supper. To the Protestant ear, Mass is best understood as a daily service of prayers in which Christians partake of the Lord's supper, and the "mass of Christ" was specially devoted to the celebration of Christ's birth.
The Development of the Liturgical Calendar
That is the simple explanation of the word Christmas. However the term is also a clue to the larger development of church tradition and practice. To begin, neither the celebration of Christ's birth nor the word "mass" existed in the Early Church. It was not until 397 that missa was used by St. Ambrose to describe the already established liturgical centerpiece of the Lord's Supper. Before then, Mass was commonly called Eucharistia.
Of greater relevance to our purposes, however, is the relative absence of any Christmas celebration for the first three centuries of the Church's existence. This absence was due to the fact that early Christians actively rejected the celebration of Christ's birth. Origen (ca. 185-254 ca.) objected on the grounds that only pagan figures in the Bible, such as Pharaoh celebrated birthdays. Furthermore, the Roman Empire celebrated the birthdays of its leaders, and it was during one of these very celebrations--Herod's birthday--that John the Baptist was beheaded.
Understandably, Christians desired to distance themselves from the pagan practice of observing birthdays. Christ was not to be confused with worldly leaders, so the church placed its greatest liturgical emphasis on Easter and Pentecost. These two significant events were honored with "ecclesiastical feasts," which "not only commemorate an event or person, but also serve to excite the spiritual life by reminding us of the event it commemorates."
Easter and Pentecost remained the primary occasions for ecclesiastical feasts until the mid-fourth century when Christmas and Epiphany were added. December twenty-fifth was established as the Nativity Feast Day, and the official Nativity Mass was the first Mass of that day, held at nine o'clock in the morning.
The "Mass of Christ" Grows in Liturgical Significance
Unlike the Western churches that observed Christmas on December twenty-fifth, the Jerusalem Church had established a tradition of celebrating Christmas on January sixth. Their celebration included a special service of Mass on the night of January sixth, and it was conducted in a church built above the cave in Bethlehem where Jesus was believed to have been born.
As an increasing number of Western pilgrims visited the Holy Land and learned of this tradition, they chose to adopt the practice for themselves. Thus in the mid-fifth century the Roman Church established a Midnight Mass in the church of St. Mary Major. This " subterranean chapel" was chosen for the Midnight Mass because it symbolized the cave in Jerusalem." It should also be noted that the hour of midnight was itself significant, since some traditions conjectured that Christ was born at midnight.
Over time, the Roman tradition of Midnight Mass spread to other Western churches. Although the morning Mass remained an essential element of the Christmas Day celebration, the Midnight Mass came to signify the beginning of Christmas Day. In fact, some Christian traditions considered it to be the distinctive Christmas service.
As this tradition developed further, the church added a third Mass at dawn, thereby establishing a tripartite celebration of Christmas: Midnight Mass remembered the appearance of the angels, Mass at Dawn commemorated the arrival of the shepherds, and the Day Mass looked forward to Christ's return.
Additionally, Christians developed a fourth Mass to be held on Christmas Eve. Christmas Eve mass developed out of the practice of vigils, which Christians commonly held "on the evening before important feasts, both universal ones such as Pentecost or local ones such as the feasts of martyrs in Roman North Africa." By the fifth century, the December twenty-fourth Mass of the evening Vigil of Christmas was added to the Western liturgies
As time went on the Christmas celebration grew in popularity, so the liturgical practices grew as well. The practice of Christmas Mass became a central fixture in the church calendar which is why, by the eleventh century, the day became known by its liturgical emphasis: Christ's Mass.
Today, the word "Christmas" is used by Protestants and Catholics alike, regardless of liturgical practice and Eucharistic belief. However, the Catholic origins of the term have been a stumbling block for some Christians. In seventeenth century England, the Puritans rejected Christmas as "unbiblical and loathed it for its 'papist' name, that is, 'Christ's Mass.'" The Catholic association was so odious to this band of Protestants that they outlawed Christmas whenever they possessed the political power to do so.
Although the Puritans reacted too harshly, they undoubtedly understood the history of "Christmas." Though a small and seemingly innocuous word, it is the product of politics, religion, controversy and jubilation, forged over centuries of liturgical growth.
 Martindale, C.C. (1908). Christmas. In The Catholic Encyclopedia. New York: Robert Appleton Company. Retrieved August 26, 2011 from New Advent: http://www.newadvent.org/cathen/03724b.htm