What is the Church? She is the body of Christ. Join to it the Head, and you have one man: The Head and the body make up one man. Who is the head? He who was born of the Virgin Mary. ... And what is His body? It is His Spouse, that is, the Church.... The Father willed that these two, the God Christ and the Church, should be one man. All men are one man in Christ, and the unity of the Christians constitutes but one man. And this man is all men, all men are this man; for all are one, since Christ is one.

St. Augustine of Hippo
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