8 Mary is definitively introduced into the mystery of Christ through this event: the Annunciation by the angel. This takes place at Nazareth, within the concrete circumstances of the history of Israel, the people which first received God's promises. The divine messenger says to the Virgin: "Hail, full of grace, the Lord is with you" (Lk. 1:28). Mary "was greatly troubled at the saying, and considered in her mind what sort of greeting this might be" (Lk. 1:29): what could those extraordinary words mean, and in particular the expression "full of grace" (kecharitoméne). If we wish to meditate together with Mary on these words, and especially on the expression "full of grace," we can find a significant echo in the very passage from the Letter to the Ephesians quoted above. And if after the announcement of the heavenly messenger the Virgin of Nazareth is also called "blessed among women" (cf. Lk. 1:42), it is because of that blessing with which "God the Father" has filled us "in the heavenly places, in Christ." It is a spiritual blessing which is meant for all people and which bears in itself fullness and universality ("every blessing"). It flows from that love which, in the Holy Spirit, unites the consubstantial Son to the Father. At the same time, it is a blessing poured out through Jesus Christ upon human history until the end: upon all people. This blessing, however, refers to Mary in a special and exceptional degree: for she was greeted by Elizabeth as "blessed among women." The double greeting is due to the fact that in the soul of this "daughter of Sion" there is manifested, in a sense, all the "glory of grace," that grace which "the Father...has given us in his beloved Son." For the messenger greets Mary as "full of grace"; he calls her thus as if it were her real name. He does not call her by her proper earthly name: Miryam (= Mary), but by this new name: "full of grace." What does this name mean? Why does the archangel address the Virgin of Nazareth in this way? In the language of the Bible "grace" means a special gift, which according to the New Testament has its source precisely in the Trinitarian life of God himself, God who is love (cf. 1 Jn. 4:8). The fruit of this love is "the election" of which the Letter to the Ephesians speaks. On the part of God, this election is the eternal desire to save man through a sharing in his own life (cf. 2 Pt. 1:4) in Christ: it is salvation through a sharing in supernatural life. The effect of this eternal gift, of this grace of man's election by God, is like a seed of holiness, or a spring which rises in the soul as a gift from God himself, who through grace gives life and holiness to those who are chosen. In this way there is fulfilled, that is to say there comes about, that "blessing" of man "with every spiritual blessing," that "being his adopted sons and daughters...in Christ," in him who is eternally the "beloved Son" of the Father. When we read that the messenger addresses Mary as "full of grace," the Gospel context, which mingles revelations and ancient promises, enables us to understand that among all the "spiritual blessings in Christ" this is a special "blessing." In the mystery of Christ she is present even "before the creation of the world," as the one whom the Father "has chosen" as Mother of his Son in the Incarnation. And, what is more, together with the Father, the Son has chosen her, entrusting her eternally to the Spirit of holiness. In an entirely special and exceptional way Mary is united to Christ, and similarly she is eternally loved in this "beloved Son," this Son who is of one being with the Father, in whom is concentrated all the "glory of grace." At the same time, she is and remains perfectly open to this "gift from above" (cf. Jas. 1:17). As the Council teaches, Mary "stands out among the poor and humble of the Lord, who confidently await and receive salvation from him."
Source: Redemptoris Mater (Vatican.va)