WHY IS MARY CALLED MOTHER OF THE CHURCH?
“This is a title, venerable brothers, not new to Christian piety; it is precisely by this title, in preference to all others, that the faithful and the Church address Mary. It truly is part of the genuine substance of devotion to Mary, finding its justification in the very dignity of the Mother of the word Incarnate.
Just as, in fact, the divine maternity is the basis for her special relationship with Christ, and for her presence in the economy of salvation brought about by Jesus Christ, thus it also constitutes the principal basis for the relations between Mary and the Church, since she is the mother of Him who, right from the time of His Incarnation in her virginal bosom, joined to Himself as head His Mystical Body which is the Church. Mary, then as mother of Christ, is mother also of all the faithful and of all the pastors.”
-Blessed Paul VI