St. Photios the Great (d. 877AD) writes:
Thus, while each holy festival both affords the enjoyment of common gifts and lights up its particular glow of grace, the present feast honoring the birth of the Virgin Mother of God easily carries off the glittering prize of seniority against every competitor. For, just as we know the root to be the cause of the branches, the stem, the fruit and the flower, though it is for the sake of the fruit that care and labor are expended on the others, and without the root none of the rest grows up, so without the Virgin’s feast none of those that sprang out of it would appear. For the resurrection was because of the death; and the death because of the crucifixion, and the crucifixion because Lazarus came up from the gates of Hell on the fourth day, because the blind saw, and the paralytic ran carrying the bed on which he had lain, and because of the rest of those wondrous deeds (this is not the time to enumerate them all) for which the Jewish people ought to have sent up glory and chanted praise, but were instead inflamed to envy, on account of which they perpetrated the Savior’s murder to their own destruction.
And this because Christ, having submitted to baptism, and having released men from their error, taught the knowledge of God in deed and word. The baptism was because of the nativity; and Christ’s nativity, to put it briefly and aptly, was because of the Virgin’s nativity, by which we are being renovated, and which we have been deemed worthy to celebrate. Thus the Virgin’s feast, in fulfilling the function of the root, the source, the foundation (I know not how to put it in a more appropriate way), takes on with good reason the ornament of all those other feasts, and it is conspicuous with many great boons, and recognized as the day of universal salvation.