Pope St. Leo the Great, Semon 21. From The Fathers of the Church: Pope Leo I, Sermons. Translated by Jane Patricia Freeland and Agnes Josephine Conway. Washington, DC: Catholic University of America Press, 1996.
Our Savior, dearly beloved, was born this day. Let us rejoice. No, there cannot rightly be any room for sorrow in a place where life has been born. By dispelling fear of death, life fills us with joy about the promised eternity. No one has been cut off from a share in this excitement. All share together a single rationale for joy. Our Lord, finding no one free of guilt, has come to liberate all. Let saints exult, for the palm [of victory] lies within their reach. Let sinners rejoice, for they have been called to pardon. Let heathens take heart, for they have been summoned to life.
God’s Son (in the “fullness of time” which the “inscrutable depths of divine wisdom” had ordained) took on human nature to reconcile it to its Maker. In that way, “the devil” who invented “death” might be overcome through that very thing which he had overcome. In the conflict undertaken on our behalf, battle was joined on the most remarkably fair terms. Omnipotent Lord engages this extremely savage enemy, not in his own majesty but in our lowliness, bringing against him the very same form and the very same nature [that had been overcome], partaker indeed in our mortality but wholly without sin. What is read about birth in general does not apply to this one: “No one is clean from stain, not even an infant, had his life on earth but lasted a single day.”
Into this unique birth, then, nothing has passed over from the concupiscence of flesh, nothing flowed from the law of sin. Chosen is a royal virgin from the shoot of David. Destined to become pregnant with the sacred fruit, she conceives an offspring (both divine and human) in her spirit—before she does so in her body. So that she might not, in being uninformed about the divine plan, become frightened by its unusual effects, she learns from conversation with an angel what work was to be accomplished in her by the Holy Spirit.
She did not believe that her honor would be compromised, she who would soon be the Mother of God. Why indeed would she have any misgivings about the Conception on account of its unusual nature? She has been promised its accomplishment through the power of the Most High. That faith upon which her confidence rested finds reinforcement through the testimony of a miracle that had come as a precursor. Elizabeth has been endowed with an unhoped-for fruitfulness. For the one who had given conception to a sterile woman could undoubtedly give it to a virgin as well.
Consequently, the Word of God, God the Son of God, who “in the beginning was with God, through whom all things were made and without whom was made nothing,” to free human beings from eternal death was himself made human. He condescended to take up our lowliness without diminishing his majesty. Remaining what he was and taking on what he was not, he united the true “form of a servant” with the “form” in which he is equal to God the Father. He grafted together both natures in such a union that glorification should not overwhelm the lower nor humbling diminish the higher.
When, therefore, the identity of each substance is preserved and they join in a single Person, majesty takes up humility, strength takes up weakness, eternity takes up mortality. To pay the debt of our condition, his inviolable nature pours forth into a vulnerable one. True God and true man are combined into the unity of the Lord. So, as suited our healing, “one” and the same “Mediator between God and human beings” was able both to die (by reason of one state) and to rise again (by that of the other). Appropriately, this birth of salvation brought no corruption whatsoever to the Virgin’s integrity, for the issuing forth of truth served as guardian over her honor.
Such, then, dearly beloved, was the Nativity that befit Christ, “the power of God and the wisdom of God.” By it he both conforms to us through humanity and rises above us through divinity. Were he not indeed true God, he could apply no remedy. Were he not indeed true man, he could not show example. Exulting angels sing at the Lord’s Birth, “Glory to God in the highest,” and proclaim, “On earth, peace to people of good will.” They indeed see the heavenly Jerusalem being constructed from all the nations of the world. How much should the lowliness of human beings rejoice over this indescribable work of divine pity when the sublimity of angels so delights in it?
As a result, dearly beloved, let us give “thanks to God the Father” through his Son, in the Holy Spirit. “Because of that great love of his with which he loved us,” he took pity on us, “and, when we were dead through our sins, he brought us to life through Christ,” so that we might be a “new creature” in him, a new handiwork. “Let us therefore put aside the old human being along with its actions.” Since we have become sharers in the Birth of Christ, let us renounce “works of the flesh.”
Realize, O Christian, your dignity. Once made a “partaker in the divine nature,” do not return to your former baseness by a life unworthy [of that dignity]. Remember whose head it is and whose body of which you constitute a “member.” Recall how you had been wrested “from the power of darkness and brought into the light and the kingdom” of God. Through the Sacrament of Baptism you were made “a temple of the Holy Spirit.” Do not drive away such a dweller by your wicked actions and subject yourself again to servitude under the devil, because your “price” is the very blood of Christ, because he “will judge” you “in truth” who has redeemed you in mercy, Christ our Lord. Amen.