The doctrine of Our Lady as the Mediatrix of all graces is a truth of faith pertaining to the universal ordinary magisterium. It maintains that all the graces of conversion and sanctification, merited by Our Lord through His passion and death on the cross, have been deposited in Mary so that she may distribute them to all men of good will, «whenever she wishes, to whom she wishes, how she wishes and how much she wishes» (St Bernard).
This mystery is not only one of her most beautiful privileges, but also a reality that profoundly affects the relationship of the spiritual Mother with us and especially her role in our work of conversion and sanctification. Saint Louis-Marie Grignion de Montfort makes it clear that true and perfect devotion to Mary is based on this truth. That devotion incarnates the doctrine of Mary as “our Mother and Mediatrix” for our personal life, for our conversion and sanctification. If God wanted to “give us everything through Mary” (St Bernard) and nothing but through Mary, God will not come nearer to us without her, and neither will we go back to God without her. If we want to live Christian lives according to the will of God, our whole life must be penetrated by Mary, directed by Mary. It is in so far as she is present in us and we strive to do everything through her, with her, in her, and for her, that God will give us His graces.
Since God does not force us to accept His redeeming action, but wants our free consent, the Blessed Virgin can exercise her role of Mediatrix in us only if we desire it, if we accept it by an act of will, by a deliberate and decisive «yes». She will do her work in us only to the extent that we give ourselves to her through an act of consecration. If we consider what we give to Our Lady by this act of consecration, we must keep in mind that there are two great objectives in our spiritual life: our relationship to God and our relationship with our neighbor.
Therefore, we give ourselves to Mary so that she may become fully our Mother and Mistress, and that we may become fully her child and slave. The principal and fundamental act of consecration contains our entire gift of ourselves to Mary. It concretely and effectively focuses on our own sanctification, our personal return to God through Mary. Then, we give ourselves to Mary so that she can take charge of our life in the world and the tasks that God wants us to accomplish. Henceforth she will be the principal cause (of course, always subordinate to God) of all our actions and our relationship with others, and accept us as instruments in her immaculate hands.
We ask her to take possession of all our faculties in order to make them channels through which she can perform in souls the marvels of conversion and sanctification, and generally “crush the head of the serpent”, “vanquish all heresies in the whole world” and thus increasingly establish the “reign of the Sacred Heart of Our Lord”.