Although Christ lived by faith, Mary's faith preceded his. In her, the long formation of faith during the two millennia of the Old Testament reached its perfection. In her, the intense quality of Abraham's faith was raised to its highest degree. And she benefitted from the whole scope of the Revelation given to Moses and the prophets, culminating with the heroic rise of the "poor of Yahweh" (Is 40-55).
Mary's faith was raised to the level necessary to give birth to the Son of God and to share his life. Thus she "conceived in her heart before conceiving in her body," as the Fathers of the Church and of the Council say. In this, she is the prototype of the faith—for the Church and for all Christian souls who personally give birth to God in their hearts and in the world.
This explains why the Fiat of the Annunciation—this supreme act of faith—is not a singular act unrelated to our life. It is the shareable inauguration of what every Christian can live, by cooperating with the continued birth of Christ here below.
Father René Laurentin (d. 2017)
Adapted from Marie, clé du mystère chrétien, Fayard, 1994