Mary’s faith can also be compared to that of Abraham, whom St. Paul calls “our father in faith” (cf. Rom. 4:12). In the salvific economy of God’s revelation, Abraham’s faith constitutes the beginning of the Old Covenant; Mary’s faith at the Annunciation inaugurates the New Covenant. Just as Abraham “in hope believed against hope, that he should become the father of many nations” (cf. Rom. 4:18), so Mary, at the Annunciation, having professed her virginity (“How shall this be, since I have no husband?”) believed that through the power of the Most High, by the power of the Holy Spirit, she would become the Mother of God’s Son in accordance with the angel’s revelation: “The child to be born will be called holy, the Son of God” (Lk. 1:35) .

–  Redemptoris Mater