He sends down from the sky water, and the channels flow according to their measure, and the torrent bears away the foam that mounts to the surface. Even so from that which they heat in the fire (metal ore etc.), craving to make ornaments or utensils, comes a scum like that. Thus does Allah show (by similitudes and parables) the truth and the falsehood (or vanity) - as for the scum it is thrown off, and as for what profits man it stays on the earth. Thus does Allah coin Similitudes (or parables)!