5 The Second Vatican Council, by presenting Mary in the mystery of Christ, also finds the path to a deeper understanding of the mystery of the Church. Mary, as the Mother of Christ, is in a particular way united with the Church, "which the Lord established as his own body." It is significant that the conciliar text places this truth about the Church as the Body of Christ (according to the teaching of the Pauline Letters) in close proximity to the truth that the Son of God "through the power of the Holy Spirit was born of the Virgin Mary." The reality of the Incarnation finds a sort of extension in the mystery of the Church-the Body of Christ. And one cannot think of the reality of the Incarnation without referring to Mary, the Mother of the Incarnate Word. In these reflections, however, I wish to consider primarily that "pilgrimage of faith" in which "the Blessed Virgin advanced," faithfully preserving her union with Christ. In this way the "twofold bond" which unites the Mother of God with Christ and with the Church takes on historical significance. Nor is it just a question of the Virgin Mother's life-story, of her personal journey of faith and "the better part" which is hers in the mystery of salvation; it is also a question of the history of the whole People of God, of all those who take part in the same "pilgrimage of faith." The Council expresses this when it states in another passage that Mary "has gone before," becoming "a model of the Church in the matter of faith, charity and perfect union with Christ." This "going before" as a figure or model is in reference to the intimate mystery of the Church, as she actuates and accomplishes her own saving mission by uniting in herself-as Mary did-the qualities of mother and virgin. She is a virgin who "keeps whole and pure the fidelity she has pledged to her Spouse" and "becomes herself a mother," for "she brings forth to a new and immortal life children who are conceived of the Holy Spirit and born of God."
Source: Redemptoris Mater (Vatican.va)