From 1921 to 1963, May 31 was the Feast of “Mary Mediatrix of All Grace.”
*Leo XIII, Encyclical, Supremi Apostolatus officio. Sept 1, 1883
We judge nothing more powerful and better for this purpose than by religion and devotion to deserve well of the great Mother of God, the Virgin Mary, who is the treasurer [sequestra] of our peace with God, and the mediatrix [administra] of graces…
Benedict XV, Encyclical, Fausto appetente die, June 29, 1921
For he [St. Dominic] knew well that Mary … has such influence with her divine Son, that He confers whatever of graces He confers on humans, does so always with her as minister and decision-maker [administra et arbitra].*
Leo XIII, Encyclical, Adiutricem
It is impossible to measure the power and scope of her offices since the day she was taken up to that height of heavenly glory in the company of her Son, to which the dignity and luster of her merits entitle her. From her heavenly abode she began, by God’s decree, to watch over the Church, to assist and befriend us as our Mother; so that she who was so intimately associated with the mystery of human salvation is just as closely associated with the distribution of the graces which for all time will flow from the Redemption.
The doctrine has a strong basis in scripture. Mary’s voice sanctified John the Baptist in the womb.
For at the moment the sound of your greeting reached my ears, the infant in my womb leaped for joy. (Luke 1:44)
Her title is prophesied in the Old Testament.
I am the mother of fair love, and of fear, and of knowledge, and of holy hope. In me is all grace of the way and of the truth, in me is all hope of life and of virtue. Come over to me, all ye that desire me, and be filled with my fruits. (Sirach 24:24-26)
Many saints and doctors from St. Augustine on up taught the doctrine.
"The Rosary is the most beautiful and richest of all prayers to the Mediatrix of all grace; it is the prayer that touches most the heart of the Mother of God. Say it each day."
–Pope Saint Pius X
Many hope that it will be the fifth Marian dogma. The Church is leaning in that direction. I hope to pray the Rosary on that day.