The Church teaches us to invoke Mary as Mediatrix of all graces. This title summarizes what the Blessed Virgin is for us, in our relations with her beloved Son: the Mediatrix of grace, of mercy, the treasurer of all the graces which Jesus mertied for us. “By the communion of sorrows and of will between Christ and Mary,” says St. Pius X, “she merited to become the dispenser of all the benefits which Jesus acquired for us by shedding His Blood” (Encyclical: Ad Diem Ilium). Mary, who was associated in the closest and most intimate way with the life, the work, and the Passion of her Son, cooperated with Him in our redemption to such an extent that the grace, which Jesus alone could merit for us condignly, was merited also by Mary, although in a secondary way and by congruity only. Thus Mary obtained real power over all the supernaural treasures acquired by her Son; and since she obtained them together with Him, she also distributes them to us with Him. Leo XIII says, “It may be affirmed that, according to God’s will, nothing comes to us without going through Mary’s hands. Just as no one can approach the Almighty Father except through the Son, so no one can approach Christ except through His Mother” (Encyclical: Octobri Mense). After Jesus, who is the only Mediator, Mary is the Mediatrix: as Jesus continually intercedes with the Father in heaven on our behalf, so Mary intercedes with Jesus for us; she obtains and dispenses to us all the graces we need. The Introit of the Mass for the Feast of Mary Mediatrix of All Graces very fittingly applies to Mary the words spoken by St. Paul about Jesus: “Let us approach the throne of grace with confidence, to obtain mercy and pardon.” Next to Jesus, Mary is really “the throne of grace,” and she can obtain everything for us from her Son. She is the omnipotentia supplex, the all-powerful intercessor: all-powerful in her prayer as Mother.
“O Blessed Lady, most holy Mother of God, full of grace, inexhaustible ocean of the intimate divine liberality and gifts of God, after the Lord of all, the Blessed Trinity, you are Lady of all; after the Paraclete, you are the new Consoler of all; and after the Mediator, you are the Mediatrix for the entire world. Behold my faith and my desire inspired by heaven; do not despise me although unworthy, neither let the ugliness of my sins suspend the immensity of your mercy, O Mother of God, O name which surpasses all my desire!” (St. Ephraem of Syria).
–From Divine Intimacy, by Fr. Gabriel of St. Mary Magdalen, O.C.D.