O Admirabile Commercium: The true Christmas exchange

Christ’s Church brings the Octave of Christmas to a close with her praising, “O admirabile commercium: O marvelous exchange! Man’s Creator has become man, born of a virgin. We have been made sharers in the divinity of Christ who humbled himself to share in our humanity.”¹ This antiphon appears once in the Catechism of the Catholic Church(CCC). At the end of a surprisingly brief section on the mystery of Christmas, we learn that “to become ‘children of God’ we must be ‘born from above’ or ‘born of God.’ Only when Christ is formed in us will the mystery of Christmas be fulfilled in us. Christmas is the mystery of this ‘marvelous exchange’: O marvelous exchange!…” (CCC §526), and then begins the First Antiphon of Evening Prayer for January 1 just cited.

The Church clearly understands that the full significance of the Nativity of the Messiah in time is incomplete without simultaneously acknowledging the new life for those now born into eternity. On Christmas morning we see how in becoming a man, the Son of God “exchanges” his heavenly privilege for humanity. Only now can humans “exchange” their mortality and sniveling little selves for the great glories and perfections of heaven. St. Paul was the first to establish this language of Christ’s substitution, “…yet for your sake he became poor, so that by his poverty you might become rich” (2 Cor 8:9; cf. 2 Cor 5:15-21). Here is the true exchange of Christmas: in becoming incarnate, assuming a human nature to himself, God grants to us in return a participation in his otherwise inaccessible divine nature.

The Catechism draws from some of the Tradition’s greatest saints to express this new way of Christian living:

The Word became flesh to make us “partakers of the divine nature” [2 Pt 1:4]: “For this is why the Word became man, and the Son of God became the Son of man: so that man, by entering into communion with the Word and thus receiving divine sonship, might become a son of God” [Irenaeus, Aduersus haereses 3.19.1]. “For the Son of God became man so that we might become God” [Athanasius, De Incarnatione §54.3]. “The only-begotten Son of God, wanting to make us sharers in his divinity, assumed our nature, so that he, made man, might make men gods” [Thomas Aquinas, Opusculum §57.1-4].²

This metaphor of the Son’s enfleshment exchanging God’s humanity for man’s divinity was arguably the most common image used in teachings on Christmas in the ancient Church. The great Church Fathers were almost unanimous in expressing the fact that at Bethlehem humanity sees not only God-made-flesh but also their own invitation to become God-like.

It no doubt sounds peculiar to our ear, but the early Church referred to this new divine agency in the human soul—what later medieval theologians would call “sanctifying grace”—as humanity’s “becoming gods,” as humanity’s deification (literally, “to be made god”). For in Christ, God has “put on” our flesh, living as a man, enabling men and women now to live in charity and in joy as does God.

St. Gregory of Nazianzus could thus provocatively exhort his congregation: “Let us seek to be like Christ, because Christ also became like us: to become gods through him since he himself, through us, became a man. He took the worst upon himself to make us a gift of the best.”³ The Church Fathers saw in this image of Christianity an attractive apologetic. The goal of the Christian faith is for human persons to appropriate and thus “become” like God. This is what Christianity promises: to adopt creatures into the Triune life of God, to make men and women by grace what Jesus Christ is by nature, namely, a beloved child of the same heavenly Father. Just as in Christ God took on human attributes, in Christ humans can now take on the divine qualities of mercy, love, insight, incorruptibility and immortality.

This “exchange” was most often associated with the Christmas mysteries. It was here in this lowly babe that the lowly themselves can now gaze upon their own eternal worth. Take, for example, Pope Leo the Great’s famous line in his Christmas Day homily in the year 440: “Realize, O Christian, your dignity. Once made a ‘partaker in the divine nature’ (2 Pet 1:4), do not return to your former baseness by a life unworthy of that dignity.”⁴ Yet this exchange language goes back much further. The earliest version of the phrase itself first appears in the first piece of Christian apologetic, theEpistle to Diognetus (dated early second century). In defending the truth of the Christian faith, the anonymous author calls the Son of God’s incarnation a “sweet exchange” and presents Christ as inverting the fallen order: for the wicked the Holy has come, for sinners the Sinless appears, for the corrupt the Incorruptible is made flesh, and for all mortals the Immortal dies.⁵ Only a few decades later, the bishop of Lyons, St. Irenaeus (quoted above as well), would come to write: “Our Lord Jesus Christ, the word of God, of his boundless love, became what we are that he might make us what he himself is.”⁶

One of the strongest advocates of this “great exchange” imagery in the ancient Church was St. Augustine of Hippo (354-430). On Christmas morning of 414, the bishop of Hippo declared that there could be “no greater grace than what has now shone upon us from God: the only Son of God has become the Son of Man, making sons and daughters of men, sons and daughters of God.”⁷ Most often Augustine named this divine descent of Christ the magna mutatio, the great transformation: “For your sakes the one who was the Son of God became the Son of man, in order that you who were the sons of men might be turned into sons and daughters of God…. You were sons of men and you have become sons and daughters of God. He has shared with us our ills, and he is going to give us his goods.”⁸ In other words, “He descended for us; let us ascend to him.”⁹ The sole purpose of this exchange of natures is to elevate human persons “up” to the very life of the Trinity: “God is with us in order that we may be with him; he who came down to us in order to be with us is at work now to draw us up to himself.”¹⁰

Augustine would also give this “great exchange” a remunerative tone. In Mary’s womb, the Son of God enacts the “divine business deal (diuina commercia), the transaction effected in this world by the heavenly dealer…. Without him, we are nothing, but in him we too are Christ.”¹¹

As evidenced in the quote from the CCC, this imagery of exchange is found throughout Thomas Aquinas as well. As he would comment on the birth of Christ as professed in the Apostles Creed, “It was no small thing that the Son of God came to us and assumed our flesh for our great advantage. In so doing he established an exchange: he assumed an animated body and deigned to be born of the Virgin so as to lavish his divinity upon us.”¹² While this was admittedly not stressed as an aspect of his thought until recent times, the exchange of God’s abasement for humanity’s perfection was a central tenet of St. Thomas’ Christology.

In one of the most beautiful pieces of twentieth-century theology, Blessed Columba Marmion, O.S.B., presents the richness of this exchange in his chapter on Christmas, “O Admirabile Commercium” in his superb Christ in His Mysteries. An Irish monk serving in Belgium, Marmion yearned to communicate this truth to a century of Christians torn asunder by world wars, economic depression, and the budding challenges brought about by the beginnings of universal mechanization and globalization. His time was not much unlike our own, and he encouraged the faithful in these words:

What the Word Incarnate gives in return to humanity is an incomprehensible gift; it is a participation, real and intimate, in his Divine nature: Largitus est nobis suam deitatem. In exchange for the humanity which he takes, the Incarnate Word gives us a share in his divinity; he makes us partakers of his divine nature.¹³

Perhaps we too then could spend this Christmas prayerfully contemplating this central Christmas truth: God has visibly become one of us in order that we may live like God. On Christmas morning this great adoption process becomes known to all: God is born in time so we can be reborn in eternity, the Son of God becomes the Son of Man, so men and women can become children of the one same Father in heaven.

St. Peter, St. Irenaeus, Athanasius, Augustine, Thomas Aquinas, Marmion and countless other saints see how only deep unity with Christ will keep the human heart from eternally fragmenting. The body of Christ is born from Mary, is continued in Mother Church’s Holy Eucharist, and is to be made manifest mystically in each of us as we gaze upon the Crib of Bethlehem.