As for zakāh, its meaning encompasses growth and increase, as with crops, although purification may also fall within its meaning. When something is cleansed of what corrupts it, it flourishes, grows, becomes sound and increases, just as crops flourish when cleared of weeds. Allah Most High says:

“Were it not for Allah’s grace and mercy upon you, not one of you would ever have been purified. But Allah purifies whom He wills.”

“He said, ‘Have you killed an innocent soul who had killed no one?’”

He also says:

“Successful indeed is the one who purifies his soul.”

And He says:

“Then go back; that is purer for you.”

Going back is a righteous deed that increases the believer in goodness and purity. He also says:

“That is purer for your hearts and their hearts.”

This avoids occasions for suspicion, which is a form of avoiding sins, staying away from them and keeping them at bay. He thus declares that this is purer for the hearts of both groups.

As for the verse we are discussing, namely His words:

“Tell the believing men to lower their gaze and guard their chastity. That is purer for them,”

lowering the gaze and guarding one’s chastity involve keeping away from the impurity of sins, as well as performing righteous deeds through which a person grows in goodness. Such conduct is purer, and zakāh encompasses purification: it involves both refraining from evil deeds and performing good deeds. For this reason, it is sometimes explained as purification and sometimes as increase and growth. Its meaning encompasses both, even when purification is mentioned alongside it, as in His words:

“Take charity from their wealth to cleanse them and purify them thereby.”

Charity brings about purification from sins and brings about zakāh, which consists in righteous deeds, just as lowering the gaze and guarding one’s chastity are purer for them