1 Corinthians 10:17

"For we, who are many, are one bread, one body." "For why speak I of communion?" saith he, "we are that self-same body." For what is the bread? The Body of Christ. And what do they become who partake of it? The Body of Christ: not many bodies, but one body. For as the bread consisting of many grains is made one, so that the grains no where appear; they exist indeed, but their difference is not seen by reason of their conjunction; so are we conjoined both with each other and with Christ: there not being one body for thee, and another for thy neighbor to be nourished by, but the very same for all. Wherefore also he adds, "For we all partake of the one bread." Now if we are all nourished of the same and all become the same, why do we not also show forth the same love, and become also in this respect one? For this was the old way too in the time of our forefathers: "for the multitude of them that believed," saith the text, "were of one heart and soul." Not so, however, now, but altogether the reverse. Many and various are the contests betwixt all, and worse than wild beasts are we affected towards each other's members. And Christ indeed made thee so far remote, one with himself: but thou dost not deign to be united even to thy brother with due exactness, but separatest thyself, having had the privilege of so great love and life from the Lord. For he gave not simply even His own body; but because the former nature of the flesh which was framed out of earth, had first become deadened by sin and destitute of life; He brought in, as one may say, another sort of dough and leaven, His own flesh, by nature indeed the same, but free from sin and full of life; and gave to all to partake thereof, that being nourished by this and laying aside the old dead material, we might be blended together unto that which is living and eternal, by means of this table.

The one who is properly said to eat the body of Christ and to drink his blood is the one who is incorporated into the unity of his body. Heretics and schismatics can receive the sacrament but to no avail—in fact, to their harm—since the result is to increase their pain rather than to curtail the length of their punishment.