Gaudet Mater Ecclesia is the title of Pope John XXIII's opening speech of the Second Vatican Council. Pope John "solemnly inaugurated" the council with this speech on October 11, 1962.
Marian references
The Feast of the Maternity of the Blessed Virgin Mary was celebrated on 11 October each year prior to the Council. The Pope invoked "the protection of the Virgin Mother of God", the "Help of Christians, Help of Bishops", over the proceedings of the Council. ==References==