Mystery of the Incarnation — Et Verbum caro factum est

The Incarnation of the Son of God is the central mystery of the Christian faith: the eternal Son of the Father, consubstantial with the Father according to divinity, assumed by the work of the Holy Spirit in the womb of the Virgin Mary the integral human nature — body and rational soul — without ceasing to be God. Two natures, divine and human, subsist in one single divine Person of the eternal Word. This truth was solemnly defined by the Council of Ephesus (431) against Nestorius, in proclaiming the Blessed Virgin Mary Theotókos — Mother of God — because what she bore according to the flesh is one single divine Person; and by the Council of Chalcedon (451) against Eutyches, in the classical formula of the four negations: the two natures are united without confusion, without mixture, without division, without separation. This union is called the hypostatic union — union in the Person of the Word. From the Incarnation proceed three admirable consequences which St Leo the Great († 461) condensed in the celebrated admirabile commercium (admirable exchange): God assumed humanity that man might be divinised by grace; the eternal Son was born in time that the sons of men might be born for eternity; He who came in the form of a servant gave power to become adoptive sons (cf. Jn 1:12). This prayer meditates the mystery from the culminating verse of the Johannine Prologue (Jn 1:14), presented trilingual EN+LA+PT, with the antiphon O admirabile commercium of the First Vespers of the Solemnity of Holy Mary Mother of God (1 January) in the traditional Roman Antiphonary.

And the Word was made flesh, and dwelt among us; and we saw his glory, the glory as it were of the only-begotten of the Father, full of grace and truth (Jn 1:14).

O eternal Son of the Father, Word through whom all things were made, you willed to be born in time, of the Virgin Mary, by the work of the Holy Spirit — you who are consubstantial with the Father before all ages. I adore you as true God, begotten not made, of the same substance as the Father; and I adore you as true man, taken from the flesh of the Virgin, like us in all things except sin.

Believing with Chalcedon that in one single divine Person the two natures inseparably subsist — without confusion, without mixture, without division, without separation —, I profess with Ephesus that Mary your Mother is truly Mother of God, because the son whom she bore is the eternal Son of the Father made man.

Grant me, O Word incarnate, three graces which from your Incarnation proceed:

• the grace of the admirabile commercium — that you assumed my humanity to divinise my soul by grace; sustain in me the divine life received in Baptism;
• the grace of adoptive sonship — that by your eternal birth from the Father you give me the power to become a son of God by faith in your name (Jn 1:12); teach me to live as a son of such a Father;
• the grace of following you to the Cross — that by your self-emptying (Phil 2:7) you showed me the way of descent which leads to exaltation; grant me the humility and the obedience which make me one with you.

You who from the Father descended to the womb of the Virgin to free us from the slavery of sin, are blessed for ages of ages. Amen.

Antiphon of the First Vespers of Holy Mary Mother of God (1 January), Roman Antiphonary:

O admirable exchange: the Creator of the human race, assuming an animate body, deigned to be born of the Virgin; and proceeding man without seed, communicated to us his divinity.