A.T. Robertson Commentary Matthew 15:11

"Not that which entereth into the mouth defileth the man; but that which proceedeth out of the mouth, this defileth the man." — Matthew 15:11 (ASV)

This defileth the man (τουτο κοινο τον ανθρωπον). This word is from κοινος which is used in two senses, either what is "common" to all and general like the Koine Greek, or what is unclean and "common" either ceremonially or in reality. The ceremonial "commonness" disturbed Peter on the housetop in Joppa (Acts 10:14). See also Ac 21:28; Hebrews 9:13. One who is thus religiously common or unclean is cut off from doing his religious acts. "Defilement" was a grave issue with the rabbinical ceremonialists. Jesus appeals to the crowd here:

Hear and understand (ακουετε κα συνιετε). He has a profound distinction to draw. Moral uncleanness is what makes a man common, defiles him. That is what is to be dreaded, not to be glossed over. "This goes beyond the tradition of the elders and virtually abrogates the Levitical distinctions between clean and unclean" (Bruce). One can see the pettifogging pretenders shrivel up under these withering words.