"Lowliness was taken. by majesty, weakness by strength, mortality by eternity. To pay the debt of our fallen state, the nature which was inviolable was united with a nature which was passible. Thus, in accordance with our needs, the one and same mediator between God and man - the man Jesus Christ - was able to die in the one nature and was incapable of death in the other.

True God, then, was born in the complete and perfect nature of true man; completely human and completely divine. By human, I mean that nature which the Creator founded in us at the beginning, and which he undertook to restore. For there was no trace whatever in our Saviour of those elements which were introduced into us by the deceiver, and to which man, when deceived, allowed entrance. Nor does it follow that because he undertook to share with us our weaknesses, he thereby shared our sins.

He took the form of a servant without stain of sin. He enhanced our humanity but did not thereby diminish his divinity. The emptying by which the invisible one made himself visible, and by which the Lord and Creator of all things willed to be one with mortal men, was a bending down in pity, not a failure of power. Accordingly, he who in the form of God was the maker of man, was himself made man in the form of a slave.

Thus the Son of God enters into the depths of this world, coming down from his heavenly throne, yet not leaving his Father's glory, begotten into a new order by a new birth.

I say a new order, because he was in his own nature invisible, but was made visible in ours. He is incomprehensible, yet he willed to be comprehended. Enduring before time began, he began to be in time. The Lord of the universe took on the form of a slave, veiling his infinite majesty. The God who cannot suffer did not disdain to be a man who can, and, immortal though he was, to subject himself to the laws of death.

For he who is true God is also true man; and there is no deception in this union, where the loftiness of God and the lowliness of man are brought together. Just as God is not changed by his act of mercy, so man is not swallowed up by the dignity. Each form acts in cooperation with the other, according to its own nature: the activity of the Word is that which is appropriate to the Word, and the flesh carries out that which is appropriate to it.

One of these is ablaze with miracles, the other is overcome by injuries. As the Word does not cease to be on an equality with the glory of the Father, so the flesh does not cease to belong to the nature of our race.

For it must always be said that the one and the same Jesus is truly Son of God, and truly son of man. He is God insofar as in the beginning he was the Word, and the Word was with God, and the Word was God. And he is man insofar as the Word became flesh and dwelt among us."

A reading from the letters of Pope St Leo the Great (Letter 28, 3-4)

Prayer

Shape us in the likeness of the divine nature of our Redeemer, whom we believe to be true God and true man, since it was your will, Lord God, that he, your Word, should take to himself our human nature in the womb of the Blessed Virgin Mary. Through Christ our Lord. 

Prepared by Pontifical University Saint Thomas Aquinas