Then answered Peter and said unto him, Declare unto us this parable.
Read Chapter 15
Cyril of Alexandria
“Without understanding” is what the Lord calls those who, like the Pharisees, make a fuss about external matters and have not yet discovered the inner life. Meats, therefore, he says, have to do with filling up the body, but they do not reach into the heart. But that which does not reach to the heart is not able to defile the faithful [genuine] man or cause him to become unclean. ...
But these things His disciples said, not as grieving for those men only, but as being themselves also slightly perplexed. But because they dared not say so in their own person, they would fain learn it by their telling Him of others. And as to its being so, hear how after this the ardent and ever-forward Peter came to Him, and says, Declare unto us this parable, Matthew 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; wherefore also he was reproved.
What then says Christ? Every plant which my heavenly Father has not planted, shall be rooted up.
This, they that are diseased with the Manichæan pest affirm to be spoken of the law; but their months are stopped by what had been said before. For if He was speaking of the law, how does He further back defend it, and fight for it, saying, Why do ye transgress the commandments of God for your tradition? And how...
Peter knew that the law did not allow the eating of all foods, and he was afraid to say to Jesus, "I too am scandalized by this saying of Thine, which appears to transgress the law." Therefore he questions Jesus, feigning ignorance.