Matt. XV. 1.
“Then came to Jesus Scribes and Pharisees, which were of Jerusalem, saying, Why do Your disciples,” etc.
Then; when? When He had wrought His countless miracles; when He had healed the infirm by the touch of the hem of His garment. For even with this intent does the evangelist mark the time, that He might signify their unspeakable wickedness, by nothing repressed.
But what means, “The Scribes and Pharisees, which were of Jerusalem?” In every one of the tribes were they scattered abroad, and divided into twelve parts; but they who occupied the chief city were worse than the others, as both enjoying more honor, and having contracted much haughtiness.
But mark, I pray you, how even by the question itself they are convicted; in not saying, “Why do they transgress the law of Moses,” but, “the tradition of the elders.” Whence it is evident that the priests were inventing many novelties, although Moses, with much terror and with much threatening, had enjoined neither to add nor take away. “For you shall not add,” says he, “unto the word which I command you this day, and you shall not take away from it.”
But not the less were they innovating; as in this instance, that one ought not to eat with unwashen hands, that we must wash cups and brazen vessels, that we must wash also ourselves. Thus, when men were henceforth, as time advanced, to be freed from their observances, at that very time they bound them with the same in more and more instances, fearing lest any one should take away their power, and wishing to strike more dread, as though they were themselves also lawgivers. The thing in fact proceeded so far in enormity, that while their own commandments were kept, those of God were transgressed; and they so far prevailed, that the matter had actually become a ground of accusation. Which was a twofold charge against them, in that they both invented novelties, and were so strict exactors on their own account, while of God they made no reckoning.
And omitting to speak of the other things, the pots and the brazen vessels (for it was too ridiculous), what seemed more reasonable than the rest, that they bring forward, wishing, as seems at least to me, in that way to provoke Him to anger. Wherefore also they made mention of the elders, in order that He, as setting them at nought, might give occasion against Himself.
But it were meet first to inquire, why the disciples ate with unwashen hands. Wherefore then did they so eat? Not as making a point of it, but as overlooking henceforth the things that are superfluous, and attending to such as are necessary; having no law to wash or not to wash, but doing either as it happened. For they that despised even their own necessary food, how were they to hold these things worth much consideration? This then having often happened unintentionally—for instance, when they ate in the wilderness, when they plucked the ears of grain—is now put forward as a charge by these persons, who are always transgressing in the great things, and making much account of the superfluous.
Source: Homilies on the Gospel of St. Matthew (New Advent)