If one thing has stuck in the consciousness of folk in our secular society
it is the celebration of Christmas, despite the attempts to secularise the matter by such as printing Christmas Cards with "Seasonal Greetings" instead of "Christmas Greetings" the word "Christmas" remains in use.
Although the festival of Christmas has been celebrated since the early days of the faith, Saints like St Athanasius (fl mid-4th Century) stressed its importance, and folk celebrated it with more vigour. St Athanasius spelt out exactly why it was important and momentous - that God - the Creator and sustained of everything that exists and is yet to exist, deigned to become man, and take on our flesh. The Immortal became mortal man in order that mortal man could become immortal. In a word the "Incarnation" - to be made flesh.
Whilst various traditions became attached to Christmas (for example; in 1441 and on other years, a Christian Latvian Brotherhood decorated a Tree for Christmas, and the tradition then spread to Germany, then by 1800 to England; Santa Claus was a bringer of gifts from early legends but only became attached to Christmas in 1821, via a Children's magazine in the USA), central to all of the celebrations is the birth of the Holy Child when the Creator shared our life, complete with all the sorrows and joys. In modern parlance this act was a "game changer" and the quality of our existence is measured by an eternal dimension.
In the words of the 1956 Carol "Mary's Boy Child, Jesus Christ"; "Hark, now hear the angels sing / A new king's born today, / And man will live for evermore / Because of Christmas Day." Michael