Tafsir of Al Imran 3:141

"And that Allah may purify those who believe": That is, to cleanse them. The root of al-tamhees (purification), as Al-Khalil stated, is the refining of a thing from every defect. It is said: "I purified (maḥaṣtu) the gold," if you have removed its dross.

The sentence is coordinated with [the verb] yattakhidha (to take/select), and the repetition of the lam [of causation] serves to emphasize this rationale. For this reason, the Majestic Name [Allah] was made manifest in a place where a pronoun might have sufficed, or [it was done] to remind [the reader] of the causality due to the separation caused by the parenthetical clause. These three matters, as our Master, the Shaykh al-Islam said, are reasons for the aforementioned alternation (mudāwalah), considering that it [the alternation] occurs upon the believers. It was mentioned first because it is what requires clarification. Perhaps the final rationale was delayed until after the parenthetical clause so that it would not be imagined that the sinful are included among the wrongdoers, or so that it might be conjoined with His saying, Exalted is He: "And destroy the disbelievers", due to the correlation between them. For in both tamhees (purification) and maḥq (destruction), there is an act of removal; yet in the former, it is the removal of traces and the clearing away of filth, while in the latter, it is the removal of the essence and the destruction of the self.

The root of al-maḥq is the diminishing of a thing little by little, from which al-muḥāq (the waning phase of the moon) is derived. The meaning is: "And He will destroy the disbelievers," leaving not a single one of them to kindle the fire. This is a rationale for the alternation, considering that it occurs against them. The intent by "them" here is a specific group: those who fought the Messenger of Allah (may Allah bless him and grant him peace) on the day of Uhud and persisted in disbelief, for Allah, the Exalted, destroyed them all.

It is also said: It is permissible for this to be a rationale for the alternation as it pertains to the believers as well. For when the disbelievers prevail at times, they become deluded, and Satan casts them into the mire of false hope and whispers to them, so they remain persistent in their disbelief, leading Allah, the Exalted, to destroy them for their sins and abide them eternally in the Fire.