[…] So now, if you want to understand the body of Christ, listen to the Apostle Paul speaking to the faithful: "You are the body of Christ, member for member." [1 Cor. 12.27] If you, therefore, are Christ's body and members, it is your own mystery that is placed on the Lord's table! It is your own mystery that you are receiving! You are saying "Amen" to what you are: your response is a personal signature, affirming your faith. When you hear "The body of Christ", you reply "Amen." Be a member of Christ's body, then, so that your "Amen" may ring true! But what role does the bread play? We have no theory of our own to propose here; listen, instead, to what Paul says about this sacrament: "The bread is one, and we, though many, are one body." [1 Cor. 10.17] Understand and rejoice: unity, truth, faithfulness, love. "One bread," he says. What is this one bread? Is it not the "one body," formed from many? Remember: bread doesn't come from a single grain, but from many. When you received exorcism, you were "ground." When you were baptized, you were "leavened." When you received the fire of the Holy Spirit, you were "baked." Be what you see; receive what you are. This is what Paul is saying about the bread. So too, what we are to understand about the cup is similar and requires little explanation. In the visible object of bread, many grains are gathered into one just as the faithful (so Scripture says) form "a single heart and mind in God" [Acts 4.32]. And thus it is with the wine. Remember, friends, how wine is made. Individual grapes hang together in a bunch, but the juice from them all is mingled to become a single brew. This is the image chosen by Christ our Lord to show how, at his own table, the mystery of our unity and peace is solemnly consecrated.
(Augustin: Sermo 272)