Pope John XXIII
Mater et Magistra §0
Mater et Magistra: On Christianity and Social Progress
0 To His Venerable Brethren the Patriarchs, Primates, Archbishops, Bishops, and all other Local Ordinaries that are at Peace and in Communion with the Apostolic See, and to the Clergy and Faithful of the entire Catholic World. Venerable Brethren and Dearest Sons, Health and Apostolic Benediction. Mother and Teacher of all nations—such is the Catholic Church in the mind of her Founder, Jesus Christ; to hold the world in an embrace of love, that men, in every age, should find in her their own completeness in a higher order of living, and their ultimate salvation. She is "the pillar and ground of the truth." (1) To her was entrusted by her holy Founder the twofold task of giving life to her children and of teaching them and guiding them—both as individuals and as nations—with maternal care. Great is their dignity, a dignity which she has always guarded most zealously and held in the highest esteem.
Source: Mater et Magistra (Vatican.va)