If we look beyond the Protestant theology of “total depravity,” man can, through the grace of free will, work in cooperation with God’s offer of grace. Mary, the Mother of God, therefore, is rightly our mediatrix, for she, not being equal to or our Redeemer nor adding anything to His atonement, is our interposing friend between God and mankind. Our Lady as mediatrix, moreover, continues to intercede for us, the Church Militant, as we navigate the rough terrain of our salvation on earth.
from The Catholic Catholicism by Fr. John Harding, S.J. (pages 165-168)