The celebration of Christmas is not mostly the remembrance of a historical event, though it is that. The Nativity of Christ is also the personal salvation of each of us and the reconciliation of the entire world to God the Creator. For Christians, celebrating Christmas begins with being in Christ: we are to be one with Him, united to His death and resurrection so that we can die with Him and rise from the dead with Him. Christmas is among the most theological of Christian Feasts. It speaks to us about God and His relationship to us and the world. It is the feast of salvation revealing the world and humans to be capable of bearing God in themselves.
“Let us become like Christ, since Christ also became like us; let us become gods because of him, since he also because of us became human. He assumed what is worse that he might give what is better. He became poor that we through his poverty might become rich. He took the form of a slave, that we might regain freedom. He descended that we might be lifted up, he was tempted that we might be victorious, he was dishonoured to glorify is, he died to save us, he ascended to draw himself to us who lay below in the Fall of sin. Let us give everything, offer everything, to the one who gave himself as a ransom and an exchange for us.” (St Gregory of Nazianzus Festal Orations, pg 59)