Ven. Alexander Schmemann on Services of Christmas in the Orthodox Church

"Within the forty days preparation the theme of the approaching Nativity is introduced in the services and liturgical commemorations, little by little. If the beginning of the fast on November 15 is not liturgically marked by any hymn, five days later, on the eve of the Feast of the Entrance of the Theotokos into the Temple, we hear the first announcement from the nine hirmoi of the Christmas Canon: "Christ is born, glorify Him!"

"With these words something changes in our life, in the very air we breathe, in the entire mood of the Church’s life. It is as if we perceive far, far away, the first light of the greatest possible joy — the coming of God into His world! Thus the Church announces the coming of Christ, the Incarnation of God, His entrance into the world for its salvation. Then, on the two Sundays preceding Christmas, the Church commemorates the Forefathers and the Fathers: the prophets and the saints of the Old Testament who prepared that coming, who made history itself into the expectation, the waiting for, the salvation and reconciliation of mankind with God. Finally, on December 20th, the church begins the Forefeast of the Nativity, whose liturgical structure is similar to the Holy Week preceding Pascha — for the birth of the Son of God as child is the beginning of the saving ministry which will lead Him, for the sake of our salvation, to the ultimate sacrifice of the Cross." (Read the whole thing here.)