Jesus was surprised that His own disciples still needed this explained. The saying was plain, yet they treated it as a riddle. Barnes says Peter meant, "Explain to us more fully this obscure and novel doctrine." Barnes adds that Jesus "wonders that they had not yet learned to judge the foolish traditions of the Jews by the decisions of common sense, and by his own instructions." The word "also" places them alongside the crowd and the Pharisees who had not understood, and "yet" points to how long they had been with Him. Gill says the saying, "though expressed in very plain words, and easy to be understood," did not appear clear to them.

Jesus asked a second question and then explained it Himself: "Do not ye yet understand, that whatsoever entereth in at the mouth goeth into the belly, and is cast out into the draught?" (Matthew 15:17). What comes out of the mouth comes "from the heart; and they defile the man" (Matthew 15:18). He listed what proceeds from the heart, from "evil thoughts" to "blasphemies," and concluded that "to eat with unwashen hands defileth not a man" (Matthew 15:19-20).

"Without understanding" is asunetos, which Thayer defines as unintelligent or without understanding. It appears only five times in the New Testament, including the parallel in Mark 7:18 and Romans 1:21, 31. The word "yet" translates akmēn, glossed "still" in the interlinear.

Peter called the saying a "parable." Barnes notes that the word sometimes means "a dark or obscure saying" (Psalm 78:2). The disciples had grown up with the clean and unclean food laws and the washing customs, so a teaching that food could not defile a man sounded new and strange to them.

This question shows both the patience and the expectations of Jesus. He expected His followers to grow in understanding through His teaching, and He was honest when they did not. Yet He did not stop at the rebuke. He explained the matter fully, step by step (Matthew 15:17-20).

Matthew Henry sees something good in Peter's request: "Where a weak head doubts concerning any word of Christ, an upright heart and a willing mind seek for instruction." The disciples were slow, but they came to Jesus to learn. That is the difference between them and the offended Pharisees.