Am I polishing a tile?

Huai-rang went into the zendo and asked Ma-tsu: "What are you aiming at by sitting there in meditation like that?"
Ma-tsu answered: "I want to become a buddha."

Huai-rang then picked up a tile and began to polish it.

Ma-tsu asked him: "What are you doing?"
Huai-rang answered: "I'm polishing this tile to make it into a mirror."
Ma-tsu replied: "How can you make a mirror by polishing a tile?"
His teacher said: "How can sitting in meditation make a buddha?"

Ma-tsu asked, "Then what would be right?"
"It is like the case of an ox pulling a cart: if the cart does not go, would it be right to hit the cart or would it be right to hit the ox?"

Ma-tsu didn't reply.

Huai-rang continued: "Do you think you are practicing sitting meditation, or do you think you are practicing sitting Buddahood? If you are practicing sitting meditation, meditation is not sitting or lying. If you are practicing sitting Buddahood, 'Buddha' is not a fixed form. In the midst of transitory things, one should neither grasp nor reject. If you keep the Buddha seated, this is murdering the Buddha; if you cling to the form of sitting, this is not attaining its inner principle."