Fussilat: (7) Those who do not give...

7. "They" is the subject and "are disbelievers" is the predicate; the second "they" is a separating pronoun (damir fasl), and "in the Hereafter" is connected to "disbelievers." The advancement [of the prepositional phrase] is for the sake of emphasis and to observe the [rhythmic] ending of the verse. The sentence is a circumstantial clause (hal) indicating that their refusal to pay Zakat is due to their total immersion in the worldly life and their denial of the Hereafter.

Interpreting Zakat according to its legal (Sharia) meaning is one of the opinions stated by Ibn al-Sa'ib, and it is narrated from Qatadah, al-Hasan, al-Dahhak, and Muqatil. It was said: Zakat here is in its linguistic sense—meaning they do not perform that which purifies their souls, which is faith and obedience. From Mujahid and al-Rabi’, it is said: they do not purify their deeds. Ibn Jarir and a group narrated from Ibn Abbas that he said regarding this: they do not say "There is no god but Allah." The same is narrated by al-Hakim al-Tirmidhi and others from Ikrimah.

The meaning in that case is: they do not purify themselves from polytheism. Al-Tayyibi chose this, saying: The meaning based on this is, "So be upright towards Him" through monotheism and the sincerity of worship to Him, the Exalted, "and seek His forgiveness" for the polytheism that preceded from you. If you do not do that, then "Woe unto you." Thus, it was replaced with the phrase "withholding the giving of Zakat" to signal that uprightness in monotheism, the sincerity of deeds to Allah the Exalted, and dissociation from polytheism is the [true] purification of the soul. This is more consistent with the composition of the sequence, and what the scholar of the Ummah [Ibn Abbas] went to was only to observe the structure [of the Quranic flow].