Catena Aurea on John 6:55–59: Augustine of Hippo

Or thus: Whereas men desire meat and drink to satisfy hunger and thirst, this effect is only really produced by that meat and drink, which makes the receivers of it immortal and incorruptible; i. e. the society of Saints, where is peace and unity, full and perfect. On which account our Lord has chosen for the types of His body and blood, things which become one out of many. Bread is a quantity of grains united into one mass, wine a quantity of grapes squeezed together. Then He explains what it is to eat His body and drink His blood: He that eateth My flesh, and drinketh My blood, dwelleth in Me, and I in him. So then to partake of that meat and that drink, is to dwell in Christ and Christ in thee. He that dwelleth not in Christ, and in whom Christ dwelleth not, neither eateth His flesh, nor drinketh His blood: but rather eateth and drinketh the sacrament of it to his own damnation.