From Apocalypse Explained ~ Emanuel Swedenborg
Not that which entereth into the mouth maketh the man unclean, but that which cometh out of the mouth, this maketh the man unclean. Whatsoever goeth into the mouth passeth into the belly, and is cast out into the draught. But the things that proceed out of the mouth come forth from the heart. Out of the heart go forth evil thoughts, murders, adulteries, fornications, thefts, false testimonies, blasphemies (Matthew 15:11, 17-19)."That which entereth into the mouth" means in the literal sense food of every kind, which, after its use in the body, goes out through the belly into the draught; but in the spiritual sense, "that which entereth into the mouth" signifies all things that enter into the thought from the memory, and also from the world, and these also correspond to food; while the things that enter into the thought, and not also into the will, do not render a man unclean; for the memory, and thought therefrom, are to man only as a way of entrance to him, since the will is the man himself. The things that merely enter the thought and go no further are cast out as it were through the belly into the draught, "the belly" signifying from correspondence the world of spirits, from which thoughts flow in with man, and the "draught" signifying hell.
It must be known that man cannot be purified from evils and the consequent falsities, unless the unclean things that are in him come forth as far as into the thought, and are there seen, recognized, discerned, and put away. This makes evident that "that which entereth into the mouth" signifies in the spiritual sense what enters into the thought from the memory and from the world; while "that which cometh out of the mouth" signifies in the spiritual sense thought from the will or from love; for the "heart," from which thought goes forth into the mouth and from the mouth, signifies man's will and love; and as the love and will constitute the whole man, for the man is such as his love is, so the things that go forth therefrom into the mouth and out of the mouth are what make the man unclean. That these are evils of every kind is evident from the things enumerated. Such is the meaning of these words of the Lord in the heavens.
(Apocalypse Explained 580:2,3)