38 The Church knows and teaches with Saint Paul that there is only one mediator: "For there is one God, and there is one mediator between God and men, the man Christ Jesus, who gave himself as a ransom for all" (1 Tim. 2:5-6). "The maternal role of Mary towards people in no way obscures or diminishes the unique mediation of Christ, but rather shows its power": it is mediation in Christ. The Church knows and teaches that "all the saving influences of the Blessed Virgin on mankind originate...from the divine pleasure. They flow forth from the superabundance of the merits of Christ, rest on his mediation, depend entirely on it, and draw all their power from it. In no way do they impede the immediate union of the faithful with Christ. Rather, they foster this union." This saving influence is sustained by the Holy Spirit, who, just as he overshadowed the Virgin Mary when he began in her the divine motherhood, in a similar way constantly sustains her solicitude for the brothers and sisters of her Son. In effect, Mary's mediation is intimately linked with her motherhood. It possesses a specifically maternal character, which distinguishes it from the mediation of the other creatures who in various and always subordinate ways share in the one mediation of Christ, although her own mediation is also a shared mediation. In fact, while it is true that "no creature could ever be classed with the Incarnate Word and Redeemer," at the same time "the unique mediation of the Redeemer does not exclude but rather gives rise among creatures to a manifold cooperation which is but a sharing in this unique source." And thus "the one goodness of God is in reality communicated diversely to his creatures." The teaching of the Second Vatican Council presents the truth of Mary's mediation as "a sharing in the one unique source that is the mediation of Christ himself." Thus we read: "The Church does not hesitate to profess this subordinate role of Mary. She experiences it continuously and commends it to the hearts of the faithful, so that, encouraged by this maternal help, they may more closely adhere to the Mediator and Redeemer." This role is at the same time special and extraordinary. It flows from her divine motherhood and can be understood and lived in faith only on the basis of the full truth of this motherhood. Since by virtue of divine election Mary is the earthly Mother of the Father's consubstantial Son and his "generous companion" in the work of redemption "she is a mother to us in the order of grace." This role constitutes a real dimension of her presence in the saving mystery of Christ and the Church.
Source: Redemptoris Mater (Vatican.va)