Matthew 15:17

The nourishment of the body being first changed into corruption, that is, having lost its proper form, is absorbed into the substance of the limbs, and repairs their waste, passing through a medium into another form, and by the spontaneous motion of the parts is so separated, that such portions as are adapted for the purpose are taken up into the structure of this fair visible, while such as are unfit are rejected through their own passages. One part consisting of fæces is restored to earth to reappear again in new forms; another part goes off in perspiration, and another is taken up by the nervous system for the purposes of reproduction of the species.

And the Lord includes herein man's two mouths, one of the body, one of the heart. For when He says, Not all that goeth into the mouth defileth a man, He clearly speaks of the body's mouth; but in that which follows, He alludes to the mouth of the heart, But those things which proceed out of the mouth, come forth from the heart, and they defile a man.

The Pharisees, as Peter made clear, begrudgingly grasped the dictum of the Lord which says, "It is not what enters the mouth that defiles a man." God indicated through Moses long ago that not everything about the use of food must be considered clean. He …

Some cavil at this, that the Lord is ignorant of physical disputation in saying that all food goes into the belly, and is cast out into the draught; for that the food, as soon as it is taken, is distributed through the limbs, the veins, the marrow, and the nerves. But it should be known, that the lighter juices, and liquid food after it has been reduced and digested in the veins and vessels, passes into the lower parts through those passages which the Greeks call 'pores,' and so goes into the draught.

What then saith Peter? He saith not, "What can this be which Thou hast said?" but as though it were full of obscurity, he puts his question. And he saith not, "Why hast thou spoken contrary to the law?" for he was afraid, lest he should be thought to have taken offense, but asserts it to be obscure. However, that it was not obscure, but that he was offended, is manifest, for it had nothing of obscurity. Wherefore also He rebukes him, saying, "Are ye also yet without understanding?" For as to the multitude, they did not perhaps so much as understand the saying; but themselves were the persons offended. Wherefore, whereas at first, as though asking in behalf of the Pharisees, they were desirous to be told; when they heard Him denouncing a great threat, and saying, "Every plant, which my heavenly Father hath not planted, shall be rooted up," and, "They are blind leaders of the blind," they were silenced. But he, always ardent, not even so endures to hold his peace, but saith, "Declare unto us this parable." What then saith Christ? With a sharp rebuke He answers, "Are ye also yet without understanding? Do ye not yet understand?" But these things He said, and reproved them, in order to cast out their prejudice; He stopped not however at this, but adds other things also, saying, "That whatsoever entereth in at the mouth goeth into the belly, and is cast out into the draught; but those things which proceed out of the mouth come forth from the heart, and they defile the man. For out of the heart proceed evil thoughts, murders, adulteries, fornications, thefts, blasphemies, false-witnessings: and these are the things that defile the man: but to eat with unwashen hands defileth not the man." Seest thou how sharply He deals with them, and in the way of rebuke? Then He establishes His saying by our common nature, and with a view to their cure. […]