Let us see first in what this mediation consists exactly and then whether it can be proved by Scripture, Tradition, and the magisterium.
We can start by just quoting the response of St. Thomas Aquinas in his Summa Theologiae1 to the question: “Is it proper to Christ (that is, does it belong to Christ alone) to be the mediator between God and man?” Yes, answers St. Thomas, quoting the verse of St. Paul in his first epistle to Timothy: “There is one God and one mediator of God and men, the man Christ Jesus” (I Tim. 2:5-6). And he explains: It belongs properly to the office of mediator to join together those between whom he is the mediator, for extremes are united by the medium between them. Now to unite men to God belongs perfectively to Christ, through whom men are reconciled to God, according to II Cor. 5: “God was in Christ reconciling the world to Himself.” And therefore only Christ is the perfect mediator between God and man, in so far as by His death He reconciled the human race to God. Thus, after the Apostle says “mediator between God and men, the man Christ Jesus,” he adds: “who gave Himself up as a redemption for all.” It is clear, then: there is only one mediator between God and man in the sense of a perfect mediator. But then St. Thomas adds, to conclude: Nothing, however, stops there being some others who are called mediators between God and man in a certain sense, that is, in so far as they cooperate in the uniting of men with God in a dispositive and ministerial manner.
Following this teaching, one of the most well-known Catholic theologians, Fr. Merkelbach, formulates the doctrine of Mary’s mediation in the following terms: The Blessed Virgin, as the New Eve, is rightly said and truly is the perpetual mediatrix between God and man: not, of course, as a principal and absolutely necessary mediatrix, but as one that is secondary and subordinated to Christ, in such a way that she cooperated in the whole work of Redemption and that without her influence no grace, after original sin, is given to us. He explains: She is not a principal or perfective mediator because Christ alone can reconcile us to God and merit for us in strict justice (condigno); nor is she an absolutely necessary mediatrix, for the mediation of Christ suffices superabundantly: The mediation of Mary is required only because it was positively decreed that it be so by the free will of God.
Our Lady’s mediation, then, is not at all opposed to that of Christ, for it is not at all on the same level: it is a simple cooperation in it that is completely dependent on it, just as the prophets and saints of the Old Testament prepared for Christ’s redemption by announcing it and praying for it, and the apostles and their successors applied it by preaching and administering the sacraments. Although Our Lady’s mediation doesn’t differ specifically from this mediation of other saints, it does transcend it, says Fr. Merkelbach, in three ways:
This, then, is what is meant by the mediation of all graces of Our Lady. Let us now look for the proofs of this doctrine in Scripture, in Tradition, and in the magisterium of the Church.
The mediation of Mary first appears in Tradition in the form of a parallel between her role in man’s salvation and the role of Eve in our ruin. The Fathers speak already in the second century of Mary in this way as “the New Eve.” About this Fr. Garrigou-Lagrange writes: “The doctrine of Mary as the second Eve was universally accepted in the second century. The Fathers who taught it then did not regard it as the fruit of personal speculation but as the traditional doctrine of the Church supported by the words of St. Paul which describe Jesus as the second Adam and oppose Him to the first as the Author of salvation to the author of the fall.…It is necessary therefore to regard the doctrine of Mary as the second Eve, associated with the redemptive work of her Son, as a divino-apostolic tradition.”
As time went on, the doctrine of Mary’s mediation became more and more explicit. Already St. Ephrem in the fourth century prays to Our Lady: “Hail, most excellent mediatrix of God and men, hail most efficacious reconciler of the whole world.”
And St. Germanus of Constantinople in the eighth century prays: “No one is ever set free from evil, but by thee, O Immaculate above all; no one is ever granted any gift, except through thee, O most chaste; no grace of mercy is ever shown to anyone, but through thee, O most worthy of all veneration.”
These few quotes give an idea of the Tradition on this subject that simply became more and more explicit and universal. The evidence from Tradition for this doctrine is stronger, says Merkelbach, than that for the Assumption, which was defined a dogma, nevertheless, solely on the basis of Tradition. Thus, he says, to deny it is “at least temerarious.”
Finally, after seeing the evidence from Scripture and Tradition for this doctrine, we can hear what the magisterium of the Church, basing itself on this evidence, teaches us. Leo XIII in Jucunda Semper (September 8, 1894) makes his own a text of St. Bernadine of Siena affirming the universal mediation of Mary: “That we seek Mary’s help by prayer, he says, rests, as upon its foundation, on that office she unceasingly exercises before God for us of obtaining us divine grace…by that law of reconciliation and prayer expressed by St. Bernadine: ‘Every grace that is communicated to this world has a threefold course. For by an excellent order, it is dispensed from God to Christ, from Christ to the Virgin, from the Virgin to us.’”
Pius XI continues this same teaching in his encyclical Miserentissimus Redemptor: “Since she gave birth to the Redeemer and offered Him as a victim on the cross, by a mysterious union with Christ and by an entirely singular grace on His part, she also was and piously is called Redemptrix. We confide in her prayers before Christ who, although He is the one ‘mediator of God and men,’ willed to accept His Mother as the advocate of sinners before Himself and the minister and the mediatrix of grace.”
The same pope calls Our Lady “the treasurer (sequestra) of all graces with God” and writes: “God alone gives the grace (needed for sanctity), but if the grace is from God, it is nevertheless given through Mary, who is our advocate and Mediatrix. God grants the graces, Mary obtains them and distributes them.” Pius XII is equally clear. In his radio message to Fatima on May 13, 1946, he says: “Having been associated, as Mother and Minister, with the King of martyrs in the ineffable work of human redemption, she is always associated, with a practically measureless power, in the distribution of the graces that derive from the Redemption.”
Let us then have recourse to our Lady, Mediatrix of All Graces!
1 III, q. 26, a. 1.
2 Benedictus Henricus Merkelbach, O.P., Mariologia, Paris, Desclée de Brouwer, 1939, III, Q. 2, a. 1.