why do we celebrate Jesus birthday on Dec 25th

Why do we celebrate Jesus birthday on Dec 25th, when it is not know exactly when he was born.

It is unknown exactly when or why December 25 became associated with Christ's birth. The New Testament does not give a specific date.[14] Tertullian does not mention it as a major feast day in the Church of Roman Africa. In 245, the theologian Origen denounced the idea of celebrating Christ's birthday "as if he were a king pharaoh". He contended that only sinners, not saints, celebrated their birthdays.[15]Sextus Julius Africanus popularized the idea that Christ was born on December 25 in his Chronographiai, a reference book for Christians written in AD 221.[11] This date is nine months after the traditional date of the Incarnation (March 25), now celebrated as the Feast of the Annunciation. March 25 was considered to be the date of the vernal equinox and therefore the creation of Adam; early Christians believed this was also the date Christ was crucified. The Christian idea that Christ was conceived on the same date that he died on the cross is consistent with a Jewish belief that a prophet lived an integral number of years.[16] Thus, the date as a birthdate for Christ is traditional, and is not considered to be his actual date of birth.

Although the identification of the birth date of Christ is debated, liturgical celebrations of the Nativity were celebrated from at least A.D. 200 in the Christian East. The earliest reference is found in St. Clement of Alexandria's writings in reference to a celebration of the Nativity and the Epiphany. [17] Another reference is found in the Chronography of 354, an illuminated manuscript compiled in Rome in 354.[1][18] In the East, early Christians celebrated the birth of Christ as part of Epiphany (January 6), although this festival focused on the baptism of Jesus.[19]

Christmas was promoted in the Christian East as part of the revival of Catholicism following the death of the pro-Arian Emperor Valens at the Battle of Adrianople in 378. The feast was introduced to Constantinople in 379, and to Antioch in about 380. The feast disappeared after Gregory of Nazianzus resigned as bishop in 381, although it was reintroduced by John Chrysostom in about 400.[1] The Twelve Days of Christmas are the twelve days from Christmas Day to the Feast of Epiphany on January 6 that encompass the major feasts surrounding the birth of Christ. In the Latin Rite, one week after Christmas Day January 1 has traditionally been the celebration the Feast of the Naming and Circumcision of Christ, but since Vatican II, this feast has been celebrated as the Solemnity of Mary, Mother of God.

I'll remember when I'm celebrating that paganism predated Jesus