Our Savior truly became human, and from this has followed the salvation of humanity as a whole. Our salvation is in no way fictitious, nor does it apply only to the body. The salvation of the whole person, that is, of soul and body, has really been achieved in the Word himself.

Our body has acquired something great through its communion and union with the Word. From being mortal it has been made immortal; though it was a living body it has beome a spiritual one; through it was made from the earth it has passed through the gates of heaven.

—Athanasius, To Epictetus 5-9

God on earth, God among us! No longer the God who gives his law amid flashes of lightning, to the sound of the trumpet on the smoking mountain, within the darkness of a terrifying storm, but the God who speaks gently and with kindness in a human body to his kindred. God in the flesh! It is no longer the God who acts only at particular instants, as in the prophets, but one who completely  assumes our human nature and through his flesh, which is that of our race, lifts all humanity up to him.

God comes in the flesh in order to destroy the death concealed in the flesh. Death reigned till the coming of Christ; but when the saving grace of God appeared…death was swallowed up in this [resurrection] victory, being unable to endure the sojourn of the true Life among us. O, the depth of the goodness of God and of his love for all of us! He is the Lord who has appeared to us, not in his divine form, in order not to terrify us in our weakness, but in the form of a servant, that he might set free what had been reduced to servitude.

Today Adam’s condemnation has bee lifted. We shall no longer say: “You are dust, and to dust you shall return,” but, “United to him who is in heaven, you shall be lifted up to heaven.”

—Basil the Great, Homily for the Birth of Christ

It would be no mistake to call [Christmas] the chief and mother of all holy days. Had Christ not been born of the flesh, he would not have been baptized, which is the theophany or manifestation. Nor would he have been crucified, which is the [Passover]. Nor would he have sent down the Spirit, which is Pentecost. Therefore, just as different rivers arise from a single source, these other feasts [Easter, the Ascension, Pentecost] have their beginnings in the birth of Christ.

—John Chrysostom, On the Incomprehensible Nature of God