If anyone wishes to live by the Spirit of Christ, let them become the body of Christ. No one lives by the Spirit of Christ except the body of Christ. My brethren, understand what I mean to say: You are a human being; and you have both a spirit and a body. (I call that a spirit which is called the soul--that which makes you human--for you consist of soul and body.) And so you have an invisible spirit and a visible body. Tell me: which lives by the other? Does your spirit live because of your body, or your body because of your spirit? Everyone living can answer (and he that cannot answer this, I know not whether he lives)! And what does everyone that lives answer? 'My body, of course, lives by my spirit!' Do you wish, then, to live by the Spirit of Christ too? Then be in the body of Christ! For surely my body does not live by YOUR spirit. My body lives by MY spirit, and your body by your spirit. So also, the body of Christ cannnot live except by the Spirit of Christ. It is for this reason that the Apostle Paul, talking about this Bread, says: "One bread." He says, "we being many are one body" (1 Corinthians 10:17).

O Mystery of piety! O Sign of unity! O Bond of charity!

He that wants to live has where to live, has whence to live. Let him draw near, let him believe; let him be embodied in Christ's body--the Church, that he may be made to live. Let him not shrink from the compact of the members; let him not be a rotten member that deserves to be cut off; let him not be a deformed member whereof to be ashamed; let him be a fair, fit, and sound member; let him cleave to the Body, live for God by God.

St. Augustine, Sermons on John: Tractate XXVI, par. 13