The Constitution on the Sacred Liturgy of the Second Vatican Council. It was the first document issued by the Council, whose purpose was expressed in the opening paragraph: ". . . to impart an ever increasing vigor to the life of the faithful; to adapt more closely to the needs of our age those institutions which are subject to change; to foster whatever can promote union among all who believe in Christ; to strengthen whatever can help to call all mankind into the Church's fold" (December 4, 1963).