A mediator is someone who is situated between two parties and seeks to bring them into accord. The mediator does have a particular position of his own but operates in a completely unselfish manner. A medium, in the sense of a psychic, refers to one who establishes contact with the supernatural world. All three senses refer to a middle through which two things are brought into contact with each other.
In Catholic Mariology, Mary is given the title “Mediatrix” to indicate that she, as Mother of God, is the medium through which flow all God’s graces. The Second Vatican Council (Lumen Gentium, 61-2) states that “she cooperated in the work of the Savior, in an altogether singular way, by obedience, faith, hope, and burning love, to restore supernatural life to souls. As a result she is our Mother in the order of grace.”
It may be said that Mary is a mediatrix of grace in three ways: first, as the Mother of God, through whom Christ came into the world; second, as the Immaculate Conception who was a sinless model for all to imitate; and, third, after her assumption through her apparitions and constant prayers interceding for all her children. Nathaniel Hawthorne had a sense of the intermediary efficacy of Mary when he wrote the following words: “I have always envied Catholics their faith in that sweet, sacred, Virgin Mother who stands between them and the Deity, intercepting somewhat His awful splendor, but permitting His love to stream more intelligibly to human comprehension through the medium of a woman’s tenderness.”