We are right to call Mary "Mother of Mercy" is that she was the one chosen to be the Mother of God — in other words, she was the Mother of the merciful Savior, and in this way she literally brought Divine Mercy Himself to birth in our world. Of course, this is nothing more than the common faith of the Church. When Mary humbly accepted the angel Gabriel's call, she actually conceived in her womb, and brought to birth into our world, the merciful God made flesh, Mercy Incarnate, Jesus Christ.
In the conclusion of his encyclical Veritatis Splendor (1993), Pope John Paul II summarized this Gospel truth for us:
Mary is Mother of Mercy because her Son, Jesus Christ, was sent by the Father as the revelation of God's mercy (cf Jn 3:16-18). Christ came not to condemn but to forgive, to show mercy (cf Mt 9:13). And the greatest mercy of all is found in His being in our midst and calling us to meet Him and to confess, with Peter, that He is "the Son of the living God" (Mt. 16:16). No human sin can erase the mercy of God, or prevent Him from unleashing all His triumphant power, if we only call upon Him. Indeed, sin itself makes even more radiant the love of the Father who, in order to ransom a slave, sacrificed His Son: His mercy toward us is Redemption. This mercy reaches its fullness in the gift of the Spirit who bestows new life and demands that it be lived. No matter how many and great the obstacles put in His way by human frailty and sin, the Spirit who renews the face of the earth (cf Ps 104:30), makes possible the miracle of the perfect accomplishment of the good. This renewal, which gives the ability to do what is good, noble, beautiful, pleasing to God and in conformity with His will, is in some way the flowering of the gift of mercy, which offers liberation from the slavery of evil and gives the strength to sin no more. Through the gift of new life, Jesus makes us sharers in His love, and leads us to the Father in the Spirit.
It is ironic that this very simple theological truth — that Mary is our Mother of Mercy because she gave birth to our merciful Savior — has now become the focal point for a modern theological controversy: the claim that as Mother of Mercy, she is also the "Co-Redemptrix," and the "Mediatrix of all graces." The issue is not as complex as these theological phrases sound. Dr. Mark Miravalle, professor of theology at Franciscan University in Steubenville, Ohio, tells of an encounter with Mother Teresa of Calcutta when she expressed the truth of the matter in all its simplicity:
Sacred Scripture profoundly reveals the role of our Blessed Mother as Co-Redemptrix. At the Annunciation, when Mary says "yes" to the angel and thereby gives her "fiat" (Lk 1:38), she gives to the Redeemer the instrument of redemption, His human body. In a discussion I had with the late Mother Teresa of Calcutta regarding the solemn papal definition of the co-redemptive role of Our Lady, within the first two minutes of speaking, Mother said, "Of course she is Co-Redemptrix, of course. She gave Jesus his body and the body of Jesus is what saved us." I replied, "Mother, that's the difference between sanctity and theology. You say in two minutes what it takes the theologians three volumes to write." (from Divine Mercy: The Heart of the Gospel, published by the John Paul II Institute of Divine Mercy, 1999).
As Mother of Mercy and Co-Redemptrix, Mary is also rightly called the "Mediatrix of all graces," and in his encyclical Redemptoris Mater (1987), Pope John Paul II called her "Mediatrix of Mercy." If we think of ourselves as the little children in God's family (and that is precisely what Jesus said we must become: like little children), then it only stands to reason that we are dependent upon the mother in God's family, Mary our Mother, to "mediate" to us (that is, to pass on to us) everything that we need. Dr. Miravalle explains for us the truth behind these exalted titles, "Mediatrix":
We see the beginning of Mary's unique sharing in the salvific mediation of Christ at the Annunciation, where the free consent of the Virgin to be the Theotokos, the "God-bearer," mediates to the world Jesus Christ, Savior and Author of all grace.
It is in virtue of Mary's yes that He who is the source and mediation of all graces of redemption came to the human family. "And the Word became flesh and dwelt among us, full of grace and truth...And from his fullness we have all received, grace upon grace" (Jn 1:14, 16). Mary's moral and physical mediation of Christ as Mother brought into the world the Uncreated Grace from which flows every grace received in his Body, which constitutes the People of God. The Church confirms: "From Him flows out into the body of the Church all light through which the faithful receive supernatural enlightenment, and every grace, through which they became holy, as He himself is holy ... (Pius XII, Mystici Corporis).
The maternal mediation of Mary in bringing to the lost world its Savior was already prophesied in the ancient prophecy (cf. Gen 3:15), where the Woman would bring to the world as Mother the seed of victory over Satan. It is Mary, the New Eve, who by freely and physically mediating the New Adam, source of our salvation in grace, becomes "for the whole human race," as St. Irenaeus tells us, "the cause of our salvation."
In short, Mary, as Mother of our merciful Savior, is rightly called the Co-Redemptrix and the Mediatrix of all His graces and mercies to us. She plays a unique and unequalled role in God's plan to shower His mercy upon us all. Like any true and loving mother, her children can be trustfully and completely dependent upon her to bring us all that we need for life and growth. And that's all that Mary's "mediation" really means. It sounds complex at first, but it's really as simple and dependable as a mother's love!