The explanation to the disciples: V. 17. And when He was entered into the house from the people, His disciples asked Him concerning the parable. V. 18. And He saith unto them, Are ye so without understanding also? Do ye not perceive that whatsoever thing from without entereth into the man, it cannot defile him; V. 19. because it entereth not into his heart, but into the belly, and goeth out into the draught, purging all meats? V. 20. And He said, That which cometh out of the man, that defileth the man.
The disciples had gotten into the habit of talking over the public teaching of the Lord, in order to find its true meaning, to get the full understanding. Here also they waited until Jesus came home with them, to the place where He, and, perhaps, they all were lodging at that time. Here they asked Him concerning this saying, which they call a parable, that is, in this case, an obscure saying, a comparison hard to understand.
The evangelist notes the full speech of Jesus, in which He told them that their lack of spiritual insight was a problem. Their stupidity is purposely made prominent, in order to bring out their need of instruction. Jesus here extends the saying, which before had touched only upon the moral sphere of man's life, in order to make His meaning still plainer. That which enters into the body from without, in the shape of food, cannot make him unclean morally or spiritually, it cannot affect the condition of his heart before God. Foods merely, generally speaking, influence the physical side of man. They are taken into the stomach, and finally the waste matter is thrown out by the body, thus actually purging the body of matter which might make him unclean.
Thus Christ incidentally extended His saying concerning ceremonial uncleanness to abolishing the distinction maintained in the Old Testament concerning the cleanness and uncleanness of various foods. He practically declared all meats to be clean; the distinction which the Jews had so rigidly and rigorously observed was hereby abrogated for the New Testament.