This is from the Rotelle series....John E. Rotelle, O.S.A., ed., WSA, Sermons, Part 3, Vol. 7, trans. Edmund Hill, O.P., (Hyde Park: New City Press, 1993), pp. 300-301.
ON THE DAY OF PENTECOST TO THE INFANTES, ON THE SACRAMENT
One thing is seen, another is to be understood. What you can see on the altar, you also saw last night; but what it was, what it meant, of what great reality it contained the sacrament, you had not yet heard. So what you can see, then, is bread and a cup; that's what even your eyes tell you; but as for what your faith asks to be instructed about, the bread is the body of Christ, the cup the blood of Christ. It took no time to say that indeed, and that, perhaps, may be enough for faith; but faith desires instruction. The prophet says, you see, Unless you believe, you shall not understand (Is 7:9). I mean, you can now say to me, You've bidden us believe; now explain, so that we may understand. Some such thought as this, after all, may cross somebody's mind: We know where our Lord Jesus Christ took flesh from; from the Virgin Mary. He was suckled as a baby, was reared, grew up, came to man's estate, suffered persecution from the Jews, was hung on the tree, was slain on the tree, was taken down from the tree, was buried; rose again on the third day, on the day he wished ascended into heaven. That's where he lifted his body up to; that's where he's going to come from to judge the living and the dead; that's where he is now, seated on the Father's right. How can bread be his body? And the cup, or what the cup contains, how can it be his blood? The reason these things, brothers and sisters, are called sacraments is that in them one thing is seen, another is to be understood. What can be seen has a bodily appearance, what is to be understood provides spiritual fruit. So if you want to understand the body of Christ, listen to the apostle telling the faithful, You, though, are the body of Christ and its members (1 Cor 12:27). So if it's you that are the body of Christ and its members, it's the mystery meaning you that has been placed on the Lord's table; what you receive is the mystery that means you. It is to what you are that you reply Amen, and by so replying you express your assent. What you hear, you see, is The body of Christ, and you answer, Amen. So be a member of the body of Christ, in order to make that Amen true.
So why in bread? Let's not bring anything of our own to bear here, let's go on listening to the apostle himself, who said, when speaking of this sacrament, One bread, one body, we being many are (1 Cor 10:17). Understand and rejoice. Unity, truth, piety, love. One bread; what is this one bread? The one body which we, being many, are. Remember that bread is not made from one grain, but from many. When you were being exorcised, it's as though you were being ground. When you were baptized it's as though you were mixed into dough. When you received the fire of the Holy Spirit, it's as though you were baked. Be what you can see, and receive what you are. That's what the apostle said about the bread. He has already shown clearly enough what we should understand about the cup, even if it wasn't said. After all, just as many grains are mixed into one loaf in order to produce the visible appearance of bread, as though what holy scripture says about the faithful were happening: They had one soul and one heart in God (Acts 4:32); so too with the wine. Brothers and sisters, just remind yourselves what wine is made from; many grapes hang in the bunch, but the juice of the grapes is poured together in one vessel. That too is how the Lord Christ signified us, how he wished us to belong to him, how he consecrated the sacrament of our peace and unity on his table. Any who receive the sacrament of unity, and do not hold the bond of peace, do not receive the sacrament for their benefit, but a testimony against themselves. Turning to the Lord, God the Father almighty, with pure hearts let us give him sincere and abundant thanks, as much as we can in our littleness; beseeching him in his singular kindness with our whole soul, graciously to hearken to our prayers in his good pleasure; also by his power to drive out the enemy from our actions and thoughts, to increase our faith, to guide our minds, to grant us spiritual thoughts, and to lead us finally to his bliss; through Jesus Christ his Son. Amen.