Tractates on the Gospel of John

¹⁸ In a word, He now explains how that which He speaks of comes to pass, and what it is to eat His body and to drink His blood. “He that eats my flesh, and drinks my blood, dwells in me, and I in him.” This it is, therefore, for a man to eat that meat and to drink that drink, to dwell in Christ, and to have Christ dwelling in him. Consequently, he that dwells not in Christ, and in whom Christ dwells not, doubtless neither eats His flesh [spiritually] nor drinks His blood [although he may press the sacrament of the body and blood of Christ carnally and visibly with his teeth], but rather does he eat and drink the sacrament of so great a thing to his own judgment, because he, being unclean, has presumed to come to the sacraments of Christ, which no man takes worthily except he that is pure: of such it is said, “Blessed are the pure in heart, for they shall see God.”