The entire liturgy of Christmas Eve is consecrated to the anticipation of the certain and sure arrival of the Savior: “Today you shall know that the Lord shall come and tomorrow you shall see His glory” (Invitatory of Matins for the Vigil of the Nativity). Throughout Advent we have seen how the preparation for Jesus’ coming became more and more precise. Isaiah, John the Baptist and the Virgin Mother appeared throughout the season announcing and foretelling the coming of the King. We learn today that Christ according to His human nature is born at Bethlehem of the House of David of the Virgin Mary, and that according to His divine nature He is conceived of the Spirit of holiness, the Son of God and the Second Person of the Trinity.
Adoration of the Magi (Gentile da Fabriano)
The certitude of His coming is made clear in two images. The first is that of the closed gate of paradise. Since our first parents were cast forth from the earthly paradise the gate has been closed and a cherubim stands guard with flaming sword. The Redeemer alone is able to open this door and enter in. On Christmas Eve we stand before the gate of paradise, and it is for this reason that Psalm 23 is the theme of the vigil:
Lift up your gates, O princes, Open wide, eternal gates, That the King of Glory may enter in. . . .