He causeth water to descend from heaven, and the brooks flow according to their respective measure, and the floods bear the floating froth: And from the metals which they melt in the fire, seeking to cast ornaments or vessels for use, there ariseth a scum like unto it: Thus God setteth forth truth and vanity. But the scum is thrown off, and that which is useful to mankind remaineth on the earth. Thus doth God put forth parables.