14 And when he had called all the people unto him, he said unto them, Hearken unto me every one of you, and understand:
15 There is nothing from without a man, that entering into him can defile him: but the things which come out of him, those are they that defile the man.
16 If any man have ears to hear, let him hear.
17 And when he was entered into the house from the people, his disciples asked him concerning the parable.
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;
19 Because it entereth not into his heart, but into the belly, and goeth out into the draught, purging all meats?
20 And he said, That which cometh out of the man, that defileth the man.
21 For from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders,
23 All these evil things come from within, and defile the man.
24 And from thence he arose, and went into the borders of Tyre and Sidon, and entered into an house, and would have no man know it: but he could not be hid.
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The Savior's words that nothing entering the mouth can defile a person are sometimes interpreted to mean that there is nothing in the world that is unclean in itself, and that nothing can harm a person except what comes out of his own heart. Yet Jesus is speaking about why nothing entering the mouth can defile a person: it passes through the person and is thereby cleansed. This statement, strange at first glance, turns out to be quite logical if we keep in mind the second part of the explanation, which speaks about what comes out of the heart. It presupposes that if a person's heart stops spewing into the world everything the Savior lists, then nothing unclean will be able to defile him.
Of course, Jesus speaks about uncleanness not in the sense of sinfulness, but in the sense in which the Torah speaks about it: as a special kind of psychophysiological and spiritual state that hinders communion with God and obstructs sanctification. It is in this sense that certain kinds of food are called unclean, or non-kosher, in the Torah. They are not bad in themselves, but they are not suitable for a person who wants to live a full spiritual life.
Perhaps this was so before the coming into the world of the Messiah, who brought the Kingdom with Him. The Kingdom is where the concepts of cleanness and uncleanness truly become irrelevant, because the fullness of relationship with God there is completely different and cannot be compared with what existed before.
For a resident of the Kingdom, nature remains nature. Until a person's full transfiguration, his physiology remains what it was before. But it no longer has the same influence on a person's spiritual state that it once had. The process of digestion no longer interferes in spiritual life. On one condition: if the heart is pure and no filth comes from it. Just as it should be for a resident of the Kingdom.