The Blessed Virgin was predestined to be the Mother of God in the eternal plan for the incarnation of God’s Word. By decree of God’s providence she was, here on earth the loving mother of the divine Redeemer, the noblest of all his companions, and the humble servant of the Lord. In conceiving Christ, in bearing him, in nursing him, in presenting him to the Father in the temple, in sharing her Son’s passion, as he was dying on the cross, by her obedience, her faith, her hope and burning love, she cooperated, in a way that was quite unique, in the work of the Savior in restoring supernatural life to souls. She is therefore a mother to us in the order of grace.
This motherhood of Mary in the order of grace—from the consent which she gave in faith at the annunciation, and which she continued to give unhesitatingly at the foot of the cross—lasts without interruption until all the elect enter into eternal fulfillment. When she was taken up into heaven, she did not lay aside this saving role but she continues by her intercession for all to gain for us the gifts of eternal salvation.
In her maternal love she cares for the brothers and sisters of her Son as they journey on earth in the midst of dangers and hardships, until they are brought safely home to the happiness of heaven.
The Blessed Virgin is thus invoked in the Church under the titles of Advocate, Auxiliatrix, Adjutrix and Mediatrix. These titles must not, however, be understood as in any way detracting from, or adding to, the dignity and effectiveness of Christ, the one Mediator.
No creature can ever be classed as an equal with the incarnate Word, the Redeemer. But just as the priesthood of Christ is shared in various ways by his ministers and his faithful people, and as the goodness of God, one though it is, is, in different ways, really shared with creatures, so also the unique mediation of Christ does not exclude but brings about a variety of shared cooperation, deriving from the one unique source.
The Church does not hesitate to acknowledge this kind of subordinate role in the person of Mary. The Church has continuous experience of its effects, and commends it to the hearts of the faithful, so that as they lean on her motherly protection they may be brought into closer union with the Mediator, our Savior.
From the dogmatic constitution on the Church of the Second Vatican Council (Lumen Gentium, nn. 61-62).