+JMJ+
But why is there a tradition that Mary specifically both holds back His anger against sinners, and all graces come though her?
In the Bible, we see that Jesus is both our Merciful Savior and Stern Judge. That always has been the traditional view of God. Look for example at the oldest known iconography of “Jesus Christ, Pantokrator” or “Almighty”.
Notice the two different expressions in Jesus’ face. On our left is His merciful side, His right (our left) face mellow, and his right (our left) hand is in the gesture of benediction. On the other side (our right side) is His just side, with His face stern and even his eyebrow notched, and his left (our right) hand holding the Book of Life, where it is written who is saved, and those whose names are not written there are thrown into the fires of hell (cf. Revelation 20:15).
Now as for Mary, her queenship is deeply rooted in Tradition, based on the Biblical promise that those who persevere in God in this life will be placed in charge “over much” (see Matthew 25), as well as the tradition of the “Mother Queen” of the Davidic Kingdom. But since not only was Mary the most faithful of all of God’ servants, but she is the mother of the King of Kings, she was given “over much” according to her faithfulness on Earth and being the Mother of God, i.e.
over the whole universe, and even the whole economy of salvation, i.e. all graces.
And yet
never was Mary, in Holy Tradition, called the Mother of Justice, but she is well loved as the Mother of Mercy:
Theologians note that she does not seem to share in any special way in the royal judicial power of inflicting punishment for sin, for Tradition calls her not the Mother of justice but the Mother of mercy, a title which is hers in virtue of her mediation of all graces. Jesus seems to have kept to Himself the reign of justice as is becoming Him Who is the ‘Judge of the living and the dead.’
source
Therefore, Mary is the Refuge of Sinners, because she never judges her children but leaves that to God, and thus she is the one who “holds back His anger against sinners.”