“He sends down water from the sky, and the valleys flow according to their measure, and the torrent carries a swelling foam. And from that which they heat in the fire, seeking ornaments or useful articles, there is a foam like it. Thus Allah illustrates truth and falsehood. As for the foam, it passes away as scum, while that which benefits people remains in the earth. Thus Allah sets forth parables.” (17)

“He sends down” means: Allah, Most High. “Water from the sky” means rain. “And the valleys flow” with that water, “according to their measure,” that is, according to their size, whether small or large. “And the torrent carries,” which results from that water, “a swelling foam.” Foam is the impurity that appears upon the surface of water, as it also appears upon the surface of a cooking pot. “Swelling” means high and rising above the water. Thus, the clear water that remains is like truth, while that which vanishes and clings to the trees and the sides of the valleys is like falsehood.

It was also said that His saying, “He sends down water from the sky,” is a parable for the Quran, while the valleys are a parable for hearts. That is, He sends down the Quran, and hearts receive from it according to the degree of certainty, understanding, doubt, and ignorance within them. This is one of the two parables. The other parable is His saying, Most High: “And from that which they heat in the fire.”

Hamzah, al-Kisa'i, and Hafs recited “they heat” with the third-person prefix, in light of His saying, Most High: “that which benefits people,” since there is no direct address here. The others recited it with the second-person prefix: “from that which you heat,” meaning, from that which you heat in the fire. Heating means placing fire beneath something in order to melt it.

“Seeking ornaments” means seeking adornment, referring to gold and silver, since ornaments are made from them. “Or useful articles” means seeking items of use, such as iron, copper, lead, and brass, which are melted and made into vessels and other things from which people benefit: “there is a foam like it.”

“Thus Allah illustrates truth and falsehood”: when these metals are melted, they too produce foam like the foam of water. Thus, the clear substance that remains of these minerals is like truth, while the foam from which no benefit is derived is like falsehood.

“As for the foam” that rises above the torrent and the molten metals, “it passes away as scum,” that is, lost and worthless. Scum is what the valley casts out of foam, and what the pot throws onto its sides. It is said that a valley casts out its refuse when it throws off its debris; and that a pot casts out foam when it boils and throws out its froth. Once it becomes still, nothing remains in it.