Tim, you seem like a good and passionate Catholic. I certainly respect your strong faith and acknowledge your right to whatever pious devotion you feel drawn to. However, I do not see anything in the posts from the folks in this thread that I would call tepid about believing our own faith…. I see good passionate Catholics trying to help a brother in faith out by answering his question.
Here are few thoughts I’ve pulled together on the topic of Mary Mediatrix of All Graces…
I think it’s important to start by reminding everyone of the weight of the various Church teaching documents… in descending order of formal authority: apostolic/dogmatic constitution, encyclical letter, encyclical epistle, apostolic exhortation, apostolic letter, letter and message. Lumen Gentium is an Apostolic Constitution which carries the great weight and would hold a higher place than the Apostolic Letters and Encyclicals frequently referenced as mentioning the idea of Mediatrix of All Graces
Lumen Gentium very purposefully stopped short of declaring Mary the Mediatrix of All Graces when it said “Therefore the Blessed Virgin is invoked by the Church under the titles of Advocate, Auxiliatrix, Adjutrix, and Mediatrix. These, however, are to be so understood that they neither take away from nor add to the dignity and efficacy of Christ the one Mediator.”
This is clear when you understand how the teaching was formed at the VII. During the daily interventions, Archbishop Corrado Mingo of Monreale, Italy argued at the Council that the title “Mediatrix” should be amplified to “Mediatrix of All Graces”, yet it was omitted from LG. Several other Council fathers made that argument as well, still it was not included. It’s a well documented fact that it was considered a compromise between disparate groups at the Council to include the title ‘Mediatrix’, let alone ‘of All Graces’. The fact that the topic was openly argued on the council floor is pretty compelling evidence that the doctrine is not fully formed, let alone universally agreed on by Church Fathers.
Also at the Council, Bishop Ancel, of Lyons, France said that title “Mediatrix” was given in LG, but at the same time it was given no endorsement, thus leaving the door open for further study as the topic is still heavily debated among theologians. "Perhaps the title ‘Mediatrix might be listed with the other titles, in order to avoid the impression that it is a privileged one’ he said.
To further reinforce the point that the doctrine was not fully formed in the Constitution…during the Council, Cardinal Alfrink of the Netherlands said “the title ‘Mediatrix’ should not be insisted upon, since it generates such great difficulties.” There was a clear divisions between the Council Fathers on whether or not to even include the title 'Mediatrix", let alone define it… And there is no mention of ‘Mediatrix of All Graces.’
Last point, the last formal action on this subject was in 1997, when, at the request of the Holy See, a commission was formed to determine whether or not a 5th Marian Dogma should be defined addressing the titles Coredemptrix, Mediatrix and Advocate. The commission unanimously decided not to define a fifth Marian dogma on those titles. You can read more about it here
miraclehunter.com/marian_apparitions/societies/PAMI/12/index.html
So….A Dogmatic Constitution holds the Church’s highest teaching authority. Lumen Gentium did not declare Mary ‘Mediatrix of All Graces.’ and purposefully omitted it from the Constitution. The Church has yet to define a teaching on Mary a ‘Mediatrix’ and the last formal action on the subject ended with a decision not to pursue a definition.
This piece of Marian devotion seems to fall in to the category of personal devotion. The Church may one day declare Mary to be "Mediatrix of All Graces’, but it does not teach that today.
