Not that which goeth into the mouth - The disciples were charged with being sinners for transgressing the tradition of the elders in eating with unwashed hands.
Christ replies that what they should eat could not render them sinners. The man, the moral agent, the soul, could not be polluted by anything that was eaten. What proceeds from the man himself, from his heart, would defile him.
Defileth - Pollutes, corrupts, or renders sinful.

Not that which goeth into the mouth defileth - This is an answer to the carping question of the Pharisees, mentioned Matthew 15:2, Why do thy disciples eat with unwashed hands? To which our Lord here replies, That what goes into the mouth defiles not the man; i.e. that if, in eating with unwashed hands, any particles of dust, etc., cleaving to the hands, might happen to be taken into the mouth with the food, this did not defile, did not constitute a man a sinner; for it is on this alone the question hinges: thy disciples eat with unwashed hands; therefore they are sinners; for they transgress the tradition of the elders, i.e. the oral law, which they considered equal in authority to the written law; and, indeed, often preferred the former to the latter, so as to make it of none effect, totally to destroy its nature and design, as we have often seen in the preceding notes.
That which cometh out of the mouth - That is, what springs from a corrupt unregenerate heart - a perverse will and impure passions - these defile, i.e. make him a sinner.

Not that which goeth into the mouth defileth the man,.... No sorts of meats, or drinks, or whatever is proper food for men, or manner of eating and drinking them, when moderately used, defile a man, or render him loathsome and odious in the sight God. This is directly opposite to the notions of the Jews, who say (d), that
"forbidden meats are unclean themselves, "and defile both body and soul".''
The first food of man was herbs; after the flood he had an allowance of the flesh of beasts, without distinction; under the Levitical dispensation, a difference of meats was enjoined to be observed; the laws respecting that distinction are now abolished, and not binding on us under the Gospel dispensation. Some scruples, about some of these things, did arise among the first Christians; but in process of time these difficulties were got over: nor is there any religion in abstinence from any sort of food; men, indeed, on a "physical" account, ought to be careful what they eat and drink, but not on a religious one; moderation in all ought to be used; and whatever is ate or drank, should be received with thankfulness, and done to the glory of God, and then no defilement can arise from hence:
but that which cometh out of the mouth, this defileth a man. It is sin, and that only, which takes its rise from the heart, lies in thought, and is either expressed by the mouth, or performed by some outward action, which defiles the man, and renders him loathsome, abominable, and odious in the sight of God. The heart is the source of all evil; the pollution of it is very early, and very general, reaching to all the powers and faculties of the soul; which shows the ignorance of some, and folly of others, that talk of, and trust to the goodness of their hearts; and also the necessity of new hearts and right spirits being formed and created; and that the sinful thoughts of the heart, and the lusts thereof, are defiling to men; and that they are sinful in God's account, and abominable in his sight; that they are loathsome to sensible sinners, and are to be repented of, and forsaken by them; and need the pardoning grace of God or otherwise will be brought into judgment. Sinful words, which, through the abundance of wickedness in the heart, come out of the mouth, have the same influence and effect: words are of a defiling nature; with these men pollute both themselves and others: the tongue, though a little member, defiles the whole body; and evil and corrupt communication proceeding out of the mouth, corrupts the best of manners, and renders men loathsome to God, and liable to his awful judgment. And this is the nature of all sinful actions; they are what God can take no pleasure in; they are disagreeable, to a sensible mind; they leave a stain, which can never be removed by any thing the creature can do; nothing short of the blood of Christ can cleanse from it; and inasmuch as they are frequently committed, there is need of continual application to it. These are now the things men should be concerned about, as of a defiling nature; and not about meats and drinks, and the manner of using them, whether with hands washed, or unwashed.
(d) Tzeror Hammor, fol. 142. 1.

Not that which goeth into the mouth defileth a man; but that which cometh out of the mouth, this defileth a man--This is expressed even more emphatically in Mark (Mark 7:15-16), and it is there added, "If any man have ears to hear, let him hear." As in Matthew 13:9, this so oft-repeated saying seems designed to call attention to the fundamental and universal character of the truth it refers to.