There is one word that defines for us, more than any other, how Mary responds to God’s plan for the redemption of the world and her indispensable role in it.

Fiat.

This is the Latin word for what in English is let it be done to me. This what Mary says in Luke 1:38, at the end of the Annunciation, in response to the promise that God would overshadow her and she would conceive God in the flesh.

The Church following the teaching of Pope St. John Paul II sees Mary’s fiat as both an exemplar of radical Christian humility as well as an indication of how she would cooperate with God in bringing about his redemption of mankind. As one scholar, Antonio Lopez, writes,

Mary’s faith, expressed in her fiat, is neither a simple acceptance nor a resignation before God’s will. Rather, ‘let it be done unto me’ expresses a joyful desire to collaborate (génoito) with whatever God has determined, even without fully understanding what this will means.

The Latin well captures Mary’s simple humility by expressing her response in a single word. Indeed, it is fitting that the single Word of God entered this world through a single word. We should expect such harmony given the reality of the Incarnation. As then-Cardinal Joseph Ratzinger observes in Mary: The Church at the Source: “Mary welcomes the Holy Spirit into herself. Having become pure hearing, she receives the Word so totally that it becomes flesh in her.”

This transformation culminates in Mary’s way of speech, which is shaped by the Word dwelling fully within her. The Church teaches that Christ constitutes the fullness of revelation—not the many words of Scripture, which are revelation, but are not revelation in its fullness. That is reserved for Christ, the Word Incarnate.

In his treatise on the Trinity, St. Augustine teaches that we refer to Christ as the Word, because of God’s perfect unity and simplicity. Unlike God, man needs many words as he searches out the truth and deliberates whether to accept it God, whose will is perfectly good and unchanging and who is Truth itself, needs only one Word in order to comprehend Himself and His plan for creation.

It follows that the closer we get to God, the simpler our own speech must become. Mary’s fiat thus represents the height of holiness. She is so united to God, the Word Incarnate, that she needs but one word to communicate her acceptance and participation in His mission.

Mary’s fiat reflects the Word Incarnate in two specific ways.

First, her humility in accepting Christ into her womb mirrors his own descent from heaven, beautifully recounted by the hymn of St. Paul,

Have among yourselves the same attitude that is also yours in Christ Jesus,
Who, though he was in the form of God,
did not regard equality with God something to be grasped.
Rather, he emptied himself,
taking the form of a slave,
coming in human likeness;
and found human in appearance,
he humbled himself,
becoming obedient to death, even death on a cross (Philippians 2:5-8).

Just as Jesus emptied Himself, so also Mary emptied herself so that she might receive God within herself. Christ was to take the form of a slave; she accepted the role of a handmaid. Again, just as Christ did not cling to ‘equality with God’ so also, neither did Mary take pride in the honor she had received. Instead, she declared, ‘My soul proclaims the greatness of the Lord.’

Second, Mary’s fiat foreshadows Christ’s own submission to the will of the Father. As John Paul II writes in his encyclical Redemptoris Mater,

There is a complete harmony with the words of the Son, who, according to the Letter to the Hebrews, says to the Father as he comes into the world: ‘Sacrifices and offering you have not desired, but a body you have prepared for me…. Lo, I have come to do your will, O God’ (Heb. 10:5-7).

Christ’s own submission of the will reached its climax in the Garden of Gethsemane, where He declared, “My Father, if it is not possible that this cup pass without my drinking it, your will be done” (Matthew 26:42).

Mary’s fiat then is ultimately a participation not just in the Incarnation but also in the Passion. And notice how during the Passion she is utterly silent: she has no need to say anything else; she has said all she needs to say. (Thanks to Antonio Lopez for highlighting her notable silence.)

Mary’s fiat does not just compel our veneration, but also our imitation. Just as she submitted to the will of God, so also are we called to utter our own fiats to the will of God.

In his article on Mary, Lopez notes that we are called to follow Mary all the way. We must adopt her way of hearing, becoming so completely receptive to the Word of God that He takes flesh within us, transforming us into His own image. And, what’s more, Mary’s fiat means she is assisting us in this process. “In this allowing, reciprocating, and carrying out love’s task, the believer is sustained and spurred on by Mary’s fiat,” Lopez writes.

Mary’s fiat then also speaks to us: it calls us to respond in kind to God’s offer, to let Him work within us—and to allow Mary to work with Him in us.