The holiday for late Roman deity Sol Invictus, the Unconquerable Sun, was celebrated on December 25. I say late Roman deity because it was under the influence of eastern religions in the late second and third centuries CE that Sol Invictus (aka, Elah Gabal, its Syrian name) came to prominence. To be more specific, the Hellenized Persian deity Mithras was also born this day (and sometimes conflated with Sol Invictus in this later period). Along with a series of Egyptian cults, Mithras and Sol Invictus were two of the great religious competitors to Christianity as monotheistic cults also coming from the east, spreading rapidly throughout the empire. Additionally, the Italian holiday Saturnalia, a holiday of merry-making, was celebrated at this time. It is no accident that the Christmas was celebrated on this day during the Christian imperial period beginning in the fourth century.
The celebration of Christmas was contested in early Christianity. For most of the first few centuries, no one even thought of celebrating the birth of Christ. Easter was the central holiday. Origen (c. 250) objected to the celebration of all birthdays because, he said, it was a pagan custom! Nevertheless, it was in the early third century that Christians began speculating on the date of the birth of Christ. Various dates were offered, including March 25, the vernal equinox, which was also assumed to be the anniversary of all creation. Others favored April 2, April 19, and May 20. It was only Julius Africanus in 221 who suggested December 25. The heterodox Basilideans favored January 6, believed to be the date of Jesus’s baptism, at which time Christ entered him, also known as the Epiphany (this holiday was made orthodox later). None of these dates was accepted above the others across Christianity, and this was a rather minor discussion still at this time.
Sometime in the second quarter of the third century, during the very beginnings of the Christianization of the empire, the Epiphany was transferred to December 25 by some churches. Over the next three centuries, ending in the 6th, most Christian churches had accepted December 25 as the birthday of Christ (the exception to this day is the Armenian church).
But why December 25? In antiquity, this was the winter solstice. (Our modern calendars now celebrate this on December 21/22, but it is close enough). The days got shorter and shorter as the sun died, until the solstice when it was born again, renewed, resurrected, heralding the beginning of new life to come, literally bringing light and life to the world.
Latter-day Saint folklore, arising from a literal reading of D&C 20:1, has favored April 6 as the actual birthday of Christ, though the traditional Christian date of December 25 has always been observed. Like some early Christians, the Spring date was favored somewhat for its symbolism of the beginning of life. However, early Christians reserved Spring symbolism of return of life to earth for the death and resurrection, and kept the symbolism of the beginning of light for the birth of Christ at the winter solstice. The cycle of the cosmos (in the northern hemisphere) thus told the story of Christ, a testimony offered by the Sun and the Earth themselves.
Restoration scriptures also testify to this cosmic truth. D&C 88:6-13 provides the most dramatic example. In verse 7, we learn: “This is the light of Christ. As also he is in the sun, and the light of the sun, and the power thereof by which it was made.” As we celebrate the return of the Sun today, let us acknowledge the birth of the Son, the true light which enters the world, the true source of warmth, life, and hope. As the Lord says in D&C 88:50: “Then shall ye know that ye have seen me, that I am, and that I am the true light that is in you, and that you are in me; otherwise ye could not abound.”