Wow! Jesus uses really strong language here. At first, he seems to be breaking the very command that he just gave about being non-judgmental. But instead, Jesus is reminding us that being non-judgmental does not mean we are undiscerning, wasteful, and silly. We are to recognize that there are some people so hardened to receiving the message that they will not listen; we are to quit wasting our time in trying to convince them. He chooses the powerful imagery of a well-known proverb to make his point. He says similar things in a softer way elsewhere. The bottom line, however, is that there comes a time when we realize that people will not hear the Gospel message. Their repeated determination not to hear and their unwillingness to respond don't mean we are to try harder, but simply to try elsewhere! Being a nonjudgmental person does not mean we refuse to "see the handwriting on the wall" and keep wasting our efforts on those who refuse to hear.