MEDIATRIX OF GRACE
The blessed Virgin in the Church
The predestination of the Blessed Virgin as Mother of God was associated with the incarnation of the divine word: in the designs of divine Providence she was the gracious mother of the divine Redeemer here on earth, and above all others and in a singular way the generous associate and humble handmaid of the Lord. She conceived, brought forth, and nourished Christ, she presented him to the Father in the temple, shared her Son's sufferings as he died on the cross. Thus, in a wholly singular way she cooperated by her obedience, faith, hope and burning charity in the work of the Saviour in restoring supernatural life to souls. For this reason she is a mother to us in the order of grace.
This motherhood of Mary in the order of grace continues uninterruptedly from the consent which she loyally gave at the Annunciation and which she sustained without wavering beneath the cross, until the eternal fulfilment of all the elect. Taken up to heaven she did not lay aside this saving office but by her manifold intercession continues to bring us the gifts of eternal salvation. By her maternal charity, she cares for the brethren of her Son, who still journey on earth surrounded by dangers and difficulties, until they are led into their blessed home. Therefore the Blessed Virgin is invoked in the Church under the titles of Advocate, Helper, Benefactress, and Mediatrix. This, however, is so understood that it neither takes away anything from nor adds anything to the dignity and efficacy of Christ the one Mediator.
No creature could ever be counted along with the Incarnate Word and Redeemer; but just as the priesthood of Christ is shared in various ways both by his ministers and the faithful, and as the one goodness of God is radiated in different ways among his creatures, so also the unique mediation of the Redeemer does not exclude but rather gives rise to a manifold cooperation which is but a sharing in this one source.
The Church does not hesitate to profess this subordinate role of Mary, which it constantly experiences and recommends to the heartfelt attention of the faithful, so that encouraged by this maternal help they may the more closely adhere to the Mediator and Redeemer."
From the Council Vatican II (Dogmatic constitution Lumen gentium, 61-62)