I have a friend who became a Universalist Unitarian Minister. For a long spell we would write letters back and forth asking each other questions of faith and compare answers. He had the idea that some day we would compile all of the letters and put them in book form but the project kind of fizzled out.
Around this time the title Mediatrix for Mary was being bandied about more than usual (though it is a title afforded her in Vatican II) and it was causing consternation in certain circles that were concerned that too much power was being given to this human. One of the questions received from my friend expressed a certain amount of uneasiness with the Catholic Church seemingly to be granting Mary a godly status, as if becoming a part of the Trinity, which of course would now be a Quadernity. Anyone the least steeped in true Catholic theology would know this is impossible to do and remain a Catholic, but there were concerns none-the-less. I find this understandable.
But God always works in concert with His people. For example He does not baptize us in secret without our knowledge, consent, and cooperation. In fact, it requires the community to do this. (You can’t baptize yourself.) So God (Who is so powerful He can work outside of His sacramental system) awaits our cooperation and man (Who is so weak he can do nothing without God’s power) must say yes to God. This is why we have a priesthood. Yet (almost) nobody thinks that having priests acting in God name, celebrating the sacraments, and speaking in His Name is taking away from God’s power or majesty. The case is the same for Mary.
Mary, for her part, said yes to God’s requests. She gave her body to house the God child. She presented Him in the temple to the Father. She raised him and stood by Him in His ministry, Passion, and death. In a “wholly singular way she cooperated by her obedience, faith, hope, and burning charity in the work of the Savior restoring supernatural life to souls.” In this way she is called our Mother, not to compete with God, but to show His power breaking into the world just as we are all called to do. Christ remains our one true Mediator, but Mary, in her singular role (as similarly any minister who baptizes brings life to a soul) plays a significant role. Her role has universal significance and continues to this day and so we call her “Advocate, Helper, Benefactress, and Mediatrix.” Her role is clearly subordinate to that of her Son, but by becoming closer to her who is so close to God, we come closer to her Son just as coming closer to the heat brings you closer to the fire.