whetstone

A person of the Way can be likened to a whetstone. When Buddhist faithful come to increase their store of spiritual merit by making offerings to the monks, it is knives being sharpened on the whetstone: the knives become sharp, but the stone is worn down by this. And yet despite this, there are still some practitioners who always worry that people may not come to sharpen their knives on this whetstone.
What a pity! So Sahn: "The Mirror of Zen"