Augustine of Hippo — as excerpted in the Catena Aurea on Matthew 26:26

“i And said, Take, eat; The Lord invites His servants to set before them Himself for food. But who would dare to eat his Lord? This food when eaten refreshes, but fails not; He lives after being eaten, Who rose again after being put to death. Neither when we eat Him do we divide His substance; but thus it is in this Sacrament. The faithful know how they feed on Christ’s flesh, each man receives a part for himself. He is divided into parts in the Sacrament, yet He remains whole; He is all in heaven, He is all in thy heart. They are called Sacraments, because in them what is seen is one thing, what is understood is another; what is seen has a material form, what is understood has spiritual fruit.”