He sent down to bring the earth to life through vegetation. He likened hearts to valleys: a large heart holds abundant knowledge, just as a large valley holds abundant water, while a small heart holds only according to its capacity, like a small valley. Thus, valleys flow according to their capacity, and hearts receive guidance and knowledge according to theirs.
Similarly, when the torrent enters hearts, it stirs up the desires and doubts within them in order to uproot and remove them, just as medicine, when taken, stirs up the body’s humors, distressing the person who drinks it. This is part of the medicine’s full benefit: it stirs them up only to remove them, for it cannot coexist with them or share their place. Thus Allah illustrates truth and falsehood.
He then mentioned the parable involving fire, saying:
“And a similar scum comes from what people heat in the fire to make ornaments or utensils.”
This is the dross that emerges when gold, silver, copper, and iron are melted. The fire draws it out, separates it, and removes it from the useful substance. It is then discarded, cast aside, and swept away. Likewise, knowledge and guidance cast desires and doubts out of the believer’s heart, discarding and driving them away, just as torrents and fire cast away foam, debris, and dross. Clear water settles at the bottom of the valley, and people draw from it to drink, grow crops, and water their livestock. Likewise, pure, untainted faith settles in the depths and very core of the heart, benefiting its possessor and others through him. Whoever does not understand these two parables, reflect on them, and recognize their intended meaning has no share in them. Allah alone grants success.
He also said in The Key to the Abode of Happiness:
13:17: “He sends down water from the sky, and valleys flow according to their capacity. The torrent carries swelling foam.”
This is the parable involving water. He likened the revelation He sent down to give life to hearts to the water He sent down from the sky. He likened the hearts that bear it to the valleys that carry torrents: a large heart holds abundant knowledge, just as a large valley holds abundant water, while a small heart, like a small valley, holds little knowledge. Thus, hearts receive this knowledge according to their capacity, just as valleys flow according to theirs.