Read as rules, the Sermon on the Mount cannot be kept. Read as a koan, it was never meant to be.
You have heard that it was said, You shall not commit adultery. But I say unto you, that whosoever looks on a woman to lust after her has committed adultery with her already in his heart. Be ye therefore perfect, even as your Father which is in heaven is perfect.
— Matthew 5:27–28, 5:48
Be ye therefore perfect, even as your Father which is in heaven is perfect.
Try to keep it. Love your enemies. Take no thought for tomorrow. Want nothing that is not yours. Look at no one with desire. Be perfect. No one has met these, and the consistency of the impossibility begins, after a while, to look deliberate. Paul saw it: I had not known sin, but by the law. The rule does not produce obedience. It produces the discovery that obedience is not available.
That is a koan’s job. A koan is an instruction built to be impossible so that the one trying to follow it is broken open by the trying. Zen has what is the sound of one hand; Galilee has be perfect. Read the passage that way once and see if it changes the emotional register. The teacher is not scolding. He is setting a problem with no solution, and watching, with something like affection, to see what you become when you finally give up solving it.
Which instruction did you fail today, and what did the failing show you that succeeding could not have?