Why don't all Christians celebrate Christmas on the same day?

We regard time linearly because we experience it this way: each day marching in a progression toward the future. We view the past similarly, only fixed as if set in amber. It's natural to imagine the birth of Jesus as we do our own birthdays: stamped on the calendar on December 25th and celebrated on its anniversary annually. 

Except in the East, where Christ's coming is observed on January 6th. How can this be?

Consider that the ancients told time in terms of the great sky clocks, sun and moon. Seasons and occasions were established according to the heavenly orbs, not to mention patterns of rainfall. Calendars were shaped by familiar cycles so crops might be planted and harvested successfully.

Another significant factor in dating was the succession of rulers. So Matthew tells us about a new star in the heavens signaling a new king's arrival, but also that this occurred during the present reign of King Herod. Luke also acknowledges who held the reins of power during this event: Roman Caesar Tiberias, Palestinian procurator Pontius Pilate, and high priests Annas and Caiaphas. Details we might prefer—day of the week, date of the month, or month itself—weren't recorded. A study of celestial anomalies of this period hasn't produced an exact calendar date for the newborn king.

As the early church spread out across many cultures, news traveled slowly. Inevitably the church experienced natural divisions and differing customs. Churches of the East and West were both improvising. The winter solstice, the longest night of darkness around December 21, was already a significant observance. It seemed fitting to celebrate the arrival of the Light of the World as days grew longer beyond the solstice. Jerusalem tradition had chosen January 6 for the celebration of this Theophany, Greek for "Divine Manifestation," and this custom was embraced throughout the Eastern churches. Many of these churches observed a sequence of "epiphanies" leading up to the great one: annunciations to Zechariah and Mary, Mary and Elizabeth's visitation, John's birth, the annunciation to Joseph, and finally the birth of Jesus. 

Meanwhile, Western Christians called this same divine manifestation by the name Epiphany, observing it in late December. In time, Eastern and Western traditions mingled to create a unified liturgical chain between Nativity and Epiphany. Choosing a precise date for a historically unknown event was less important than preparing to receive this manifestation with minds and hearts fully awake.

Scripture: Exodus 23:14-17; Leviticus 23:1-44; Deuteronomy  26:1-3; 1 Maccabees 4:56-59; Ecclesiastes 1:4–7, 9-10; 3:1-8; Hosea 2:13; Zechariah 14:6-9; Mark 1:14-15; Matthew 2:1-2; Luke 3:1-2; John 1:1-5, 14

Books: Days of the Lord: The Liturgical Year, Vol. 1: Advent, Christmas, Epiphany (Liturgical Press, 1991)

Biblical Meditations for Advent and the Christmas Season, by Carroll Stuhlmueller, CP (Paulist Press, 1980)

Reprinted with permission from PrepareTheWord.com. ©TrueQuest Communications.