13 How can Faustus think that we resemble the Manichæans in attaching sacredness to bread and wine, when they consider it sacrilege to taste wine? They acknowledge their god in the grape, but not in the cup; perhaps they are shocked at his being trampled on and bottled. It is not any bread and wine that we hold sacred as a natural production, as if Christ were confined in grain or in vines, as the Manichæans fancy, but what is truly consecrated as a symbol. What is not consecrated, though it is bread and wine, is only nourishment or refreshment, with no sacredness about it; although we bless and thank God for every gift, bodily as well as spiritual.
According to your notion, Christ is confined in everything you eat, and is released by digestion from the additional confinement of your intestines. So, when you eat, your god suffers; and when you digest, you suffer from his recovery. When he fills you, your gain is his loss. This might be considered kindness on his part, because he suffers in you for your benefit, were it not that he gains freedom by escaping and leaving you empty. There is not the least resemblance between our reverence for the bread and wine, and your doctrines, which have no truth in them.
To compare the two is even more foolish than to say, as some do, that in the bread and wine we worship Ceres and Bacchus. I refer to this now, to show where you got your silly idea that our fathers kept the Sabbath in honor of Saturn. For as there is no connection with the worship of the Pagan deities Ceres and Bacchus in our observance of the sacrament of the bread and wine, which you approve so highly that you wish to resemble us in it, so there was no subjection to Saturn in the case of our fathers, who observed the rest of the Sabbath in a manner suitable to prophetic times.
Source: Reply to Faustus the Manichaean (New Advent)