He sends down water from the cloud , then watercourses flow ( with water ) according to their measure , and the torrent bears along the swelling foam , and from what they melt in the fire for the sake of making ornaments or apparatus arises a scum like it ; thus does Allah compare truth and falsehood ; then as for the scum , it passes away as a worthless thing ; and as for that which profits the people , it tarries in the earth ; thus does Allah set forth parables .