As I write, tomorrow (December 25) is Christmas, one of the most important holidays on the Christian religious calendar; the term itself derives from the phrase “Christ’s Mass.” The holiday (or “holy day”) is widely celebrated, even among non-Christians, as a festive annual occasion of gift giving, good will, and general merriment.

Secular observances of the holiday tend to focus more upon its associations with Santa Claus, big dinners, and colorfully wrapped presents beneath colorfully lit and decorated Christmas trees. But for Christians, the primary meaning of Christmas is, of course, the reverent commemoration of the birth of Jesus Christ.

Most of the world’s 2.2 billion Christians celebrate Christmas each year on December 25, but not all do. Some Eastern Orthodox churches instead observe Christmas on January 7. This is because some such Orthodox churches adhere to the older Julian calendar, instead of following the newer Gregorian calendar currently in widespread use today. (Jan 7 on the Gregorian calendar actually corresponds to Dec 25 on the older Julian calendar.)

But there is nothing particularly sacred, or even particularly Christian, about the date of December 25. The Bible nowhere specifies the actual date — or even the season — of Jesus’s birth. Some scriptural clues suggest that a date in a season other than winter may actually be more likely. The Church only adopted Dec 25 as its date for Christmas in the 4th century, perhaps in part due to that date’s proximity to already long-established and widely observed pagan winter solstice festivals (such as Yule), celebrating the “rebirth” of the Sun.

Some other traditional elements now associated with Christmas also have pre-Christian roots, and have long since been transformed and “Christianized” after being absorbed from pagan religious customs. For instance, Christmas trees and evergreen wreaths may have been adopted originally from winter solstice rites; where they previously served as pagan symbols of fertility and of life persisting through the cold dead of winter, they are now meant to suggest the eternal life of salvation in Christ.

The particular date may be arbitrary or borrowed, and some of the customs may have been adopted and adapted, but of course what really counts is the current meaning that all of these things have come to hold today, among those who religiously observe this date and these customs. And there is certainly no ambiguity there. Christians explicitly observe traditional Christmas customs on Dec 25 as part of their celebration of the birth of Christ, regardless of exactly when that birth might actually have occurred, or what some of those customs might previously have represented.

To my Christian friends and readers everywhere, may I take this opportunity to wish you all a very Merry Christmas!