"O admirabile commercium: O marvellous 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.” Thus the antiphon for First Vespers of January 1 expresses the mystery of the Incarnation. And the “Mass” part of the Christ-Mass season perpetuates this mystery and continues to invite us to live it as the finality of our daily existence. For at the offertory of every Mass, as he mingles a drop of water with the wine in the chalice, the priest prays quietly on our behalf that “By the mystery of this water and wine, we may come to share in the divinity of Christ, who humbled himself to share in our humanity.”
A child in the manger has transformed our nature by commingling it with his own, so that we only truly inhabit that nature when we love and glorify God. It is not that God has exchanged divinity for humanity. Here the word commercium has a dynamic meaning, more like the way we might use the word “commerce” to express a more lasting arrangement, like a trade deal, which is mutually beneficial. He has established the means whereby his divine love can henceforth be present in a sinful human without forcing human autonomy, a way that invites us, finite and sinful as we are, to discover his love to be as real as we are real. The means is also the message. The Word became Flesh that the flesh might become word, as Jean Vanier said.
Eternal love takes on the tenderest, least threatening and most dependent human form in the hope of finding a welcome in our hearts. So much does God love us that in Jesus he allows Himself to need us; he wants to feel our embrace, to have us understand his cries and to compassionate his distress so that by accepting Him we discover we have something to offer; we own our dignity.
Even if there were some other way of healing the breach caused by Adam’s sin, there can be no real love if it is impossible to give the beloved anything, or where the other is self-sufficient. This is part of the wondrous exchange, that God incarnates his love so that we might know it. By freely desiring what God desires to give, we ourselves become a gift to him. Albeit that our love is like water to wine: once commingled they become one.
The Catechism of the Catholic Church quotes the Christmas antiphon and tells us 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 beginning of this “marvellous exchange”, but only the beginning. God humbles himself to share in our humanity, but he will pour out that humanity in self-gift on the Cross, taking flesh to offer our flesh in sacrifice and he will perpetuate that offering to the end of time. The vulnerability of the child in the manger is the nakedness of the manhood crucified or the raised-up Host: divinity suppliant for human love.
In humbling himself thus he permits us a new, truly human way of loving.
My part of the exchange cannot be a kind of religious window-shopping. It must be to claim the self-gift of God with all I have to give him. In the words of the poet Elizabeth Jennings: “O if God begs,/ then we all hold/ Him in our power …/ We carry him/ And hear his heart/ And bring him home.”
