Matthew 15:12 – 21
 Then came his disciples, and said unto him, Knowest thou
that the Pharisees were offended, after they heard this saying?
But he answered and said, Every plant, which my heavenly Father hath
not planted, shall be rooted up. Let them alone: they be
blind leaders of the blind. And if the blind lead the blind, both shall
fall into the ditch. Then answered Peter and said unto
him, Declare unto us this parable. And Jesus said, Are ye
also yet without understanding? Do not ye yet
understand, 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, false witness,
blasphemies: These are the things which defile a man: but
to eat with unwashen hands defileth not a man. Then
Jesus went thence, and departed into the coasts of Tyre and Sidon.
St. John Chrysostom in his Homily 51 on Matthew said:
"What then says Christ? He did not remove the offense in respect of them, but reproved them, saying, 'Every plant which my heavenly Father has not planted, shall be rooted up.' (Matt.15:13) For He is wont both to despise offenses, and not to despise them. Elsewhere, for example, He says, 'But lest we should offend them, cast a hook into the sea:' (Matt.17:27) but here He says, 'Let them alone, they be blind leaders of the blind: and if the blind lead the blind, both shall fall into the ditch.' But these things His disciples said, not as grieving for those men only, but as being themselves also slightly perplexed…they dared not say so in their own person, they would fain learn it by their telling Him of others…hear how after this ardent and ever-forward Peter came to Him, and says, 'Declare unto us this parable,' (Matt.15:15) discovering the trouble in his soul, and not indeed venturing to say openly, 'I am offended,' but requiring that by His interpretation he should be freed from his perplexity…"
"'They are blind leaders of the blind.' Whereas, had He spoken it of the law, He would have said, 'It is a blind leader of the blind.' But not so did He speak, but, 'They are blind leaders of the blind:' freeing it from the blame, and bringing it all round upon them. Then to sever the people also from them, as being on the point of falling into a pit by their means, He says, 'If the blind lead the blind, both shall fall into the ditch.' It is a great evil merely to be blind, but to be in such a case and have none to lead him, nay, to occupy the place of a guide, is a double and triple ground of censure. For if it be a dangerous thing for the blind man not to have a guide, much more so that he should even desire to be guide to another."
"What then says Peter? He says not, "What can this be which you have said?" but as though it were full of obscurity, he puts this question. And he says not, 'Why have you spoken contrary to the law?' for he was afraid, lest he should be thought to have taken offense, but asserts it to be obscure…He [Jesus] rebukes him…'Are ye also without understanding?' (Matt 15:16) 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 (v.17-20)…do you see how sharply He deals with them, and in the way of rebuke?"
"Let us learn then what are the things that defile the man; let us learn, and let us flee them. For even in the church we see such a custom prevailing among the generality, and men giving diligence to come in clean garments, and to have their hands washed; but how to present a clean soul to God, they make no account…wash…not with water only, but instead of water, with all virtues. For the filth of the mouth is evil speaking, blasphemy, reviling, angry words, filthy talking, laughter, jesting…"
"Weep, groan, give alms, apologize to him that is affronted, reconcile him to yourself hereby, wipe clean your tongue, lest you provoke God more grievously…watch your tongue more than the apple of your eye. The tongue is a royal steed. If then thou put a bridle on it, and teach it to pace orderly, the King will rest and take His seat thereupon; but if you suffer it to rush about unbridled and leap wantonly, it becomes a beast for the devil and bad spirits to ride on…"
Augustine the Wise wrote in Contra Faustum, Book XVI:
"….in their desire to observe their own traditions, they did not understand the commandments of God…He [Jesus] did not speak plainly and literally, but, as usual, wished to convey some instruction under the guise of a parable…He rebukes them for not understanding His plain language, and for thinking it a parable when it was not…Here we have a complete exposure of the falsehood of the Manicheans: for it is plain that the Lord did not in this matter teach one thing to the multitude, and another in private to His disciples. Here is abundant evidence that the error and deceit are in the Manicheans, and not in Moses, nor in Christ, nor in the doctrine taught figuratively in one Testament and plainly in the other – prophesied in one, and fulfilled in the other…the reason the Jews did not believe in Christ, was because they did not observe even the plain literaly precepts of Moses. So Christ says to them: 'You pay tithe of mind and cummin, and omit the weightier matters of the law, mercy and judgment. You strain out a gnat and swallow a camel. These ought ye to have done, and not to leave the other undone.'" (Matt.23:23-24)