John Gill Commentary Matthew 15:12

"Then came the disciples, and said unto him, Knowest thou that the Pharisees were offended, when they heard this saying?" — Matthew 15:12 (ASV)

Then came his disciples, and said to him
That is, after he had dismissed the people, and was come into a private house; see (Mark 7:17) his disciples came to him, being alone, full of concern, for what he had said to the Pharisees, and before all the people; and not so well understanding it themselves.

Do you know that the Pharisees were offended after they heard this
saying?
That they set aside the commandments of God, by observing the traditions of the elders; or that they were hypocrites; and that the prophecy of Isaiah, which describes such persons, belonging to them; or that not what goes into, but what comes out of a man, defiles him: whichever it was they have respect to, or it may be to the whole.

They seem to wish Christ had not said it; because the Pharisees were, as they thought, grieved and troubled at it, as being contrary to true religion and piety; and lest they should be so stumbled, as no more to attend, and so all hopes of bringing them over to the faith of Christ be lost; and chiefly, because they perceived they were made exceeding angry, and were highly provoked; so that they might fear that both Christ, and they themselves, would feel the effects of their wrath and rage.

And perhaps it was with some such view, that he would take some prudential step that he might not fall into their hands, that they acquaint him with it.