Nothing outside a person can defile them by going into them. Rather, it is what comes out of a person that defiles them.
John Wesley
There is nothing entering into a man from without which can defile him - Though it is very true, a man may bring guilt, which is moral defilement, upon himself by eating what hurts his health, or by excess either in meat or drink yet even here the pollution arises from the wickedness of the heart, and is just proportionable to it. And this is all that our Lord asserts.
John Gill
There is nothing from without a man,.... As any sort of food and drink, whether it be received, with, or without washing of the hands:
that entering into him can defile him; in a moral sense, or render him loathsome and unacceptable in the sight of God:
but the things which come out of him; the Arabic version reads, "out of the mouth of man", as in Matt 15:11, for the things are, all sinful words which proceed from the imaginations and lusts of the heart; as all idle, unchaste, blasphemous, and wrathful words and expressions: and may include evil thoughts, words, and actions; which actions first in thought, take their rise from the corrupt heart of man; and in word, come out of the mouth; and in action, are performed by some one or other of the members of the body: these are
they that defile the man: his mind and conscience, the faculties of his soul, and the members of his body; and render him abominable in the sight of God, and expose him to his wrath and displeasure; see on Mt 15:11. The sense of the whole is, that not what a man eats and drinks, and in whatsoever way he does either, though he may eat and drink with unwashen hands, or out of cups, pots, and platters, not properly washed, according to the traditions of the elders, renders him a polluted sinful man, in the sight of God; or such as one, whose company and conversation are to be, avoided by good men; but that it is sin in the heart, and what proceeds from it; as all evil thoughts, wicked words, and impure actions; which denominate a man filthy and unclean, and expose him to the abhorrence of God, and of his people: the words may be rendered, "there is nothing from without a man, can make him common"; that is, as a plebeian, a vulgar common man, a sinful wicked man, as the common people were, or at least were so esteemed by the Pharisees; nothing that he took into his body, by eating or drinking, could put him into the class of such persons: "but the things which come out of him"; out of his heart, by his lips: "those are they that make a man common"; or a vulgar wicked man. The Ethiopic version renders it, "it is not what enters from without into the mouth of man, which can defile him; but only what goes out of the heart man, this defiles the man": the Persic version adds, "and is the sin of death"; or sin unto death, a deadly, mortal sin.
