For the Jews, boasting themselves to be the portion of God, call common those meals which all men use, as shellfish, hares, and animals of that sort. Not even however what is offered to idols is unclean, in as far as it is food and God’s creature; it is the invocation of devils which makes it unclean; and He adds the cause of it, saying, “Because it entereth not into his heart.”
The principal seat of the soul according to Plato is the brain, but according to Christ, it is in the heart.
Gloss [ed. note: It is probable that most, if not all the Glosses which cannot be found, are from St. Thomas himself, and this one is especially like his language, as may be seen by referring to Summa, 2, 2, Q148, Art 1, and 1, Q119, Art 1, in both of which places also he quotes the passages in St. Matthew parallel to this part of St. Mark.] It says therefore into his heart, that is, into his mind, which is the principal part of his soul, on which his whole life depends; wherefore it is necessary, that according to the state of his heart a man should be called clean or unclean, and thus whatsoever does not reach the soul, cannot bring pollution to the man.
Meats therefore, since they do not reach the soul, cannot in their own nature defile a man; but an inordinate use of meats, which proceeds from a want of order in the mind, makes men unclean.
But that meats cannot reach the mind, He shews by that which He adds, saying, “But into the belly, and goeth out into the draught, purging all meats.” This however He says, without referring to what remains from the food in the body, for that which is necessary for the nourishment and growth of the body remains. But that which is superfluous goes out, and thus as it were purges the nourishment, which remains.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).