Tafsir of Fussilat 41:3

"A Book" – Al-Zajjaj and Al-Hawfi narrated that this is a substitute (badal) for the preceding [implicit] grammatical element, or another predicate (khabar), or a predicate for a deleted subject. In all these possibilities, the sentence "whose verses have been detailed" occupies the position of an adjective (sifah) for the "Book."

The attribution of this "revelation" (tanzil) specifically to "The All-Merciful, the Ever-Merciful" (Al-Rahman, Al-Rahim) among all His names, serves to signal that this Book is the axis upon which both religious and worldly interests revolve, and that it has come into existence according to the dictates of Divine Mercy, as indicated by His, the Exalted’s, saying: "And We have not sent you except as a mercy to the worlds."

The "detailing" (tafsil) of its verses refers to distinguishing them verbally by their pauses and intervals, the beginnings and endings of the Surahs, and their meanings—being promises, warnings, stories, and rulings, among other things. Indeed, whoever is fair-minded knows that in the history of creation, there has never been a book that gathered within it such diverse sciences, investigations, expressions, and allusions as the Quran.

Al-Suddi said: "whose verses have been detailed" means clarified, by separating its prohibitions from its permissions, its warnings from its commands, and its promises from its threats. Al-Hasan said: Detailed by way of promises and warnings. Sufyan said: By way of rewards and punishments. What we mentioned first is more comprehensive, and perhaps what they mentioned is by way of illustration, not exclusion.

It is also said: The meaning is that its verses were detailed in their revelation, meaning they were not revealed all at once; however, this is not a strong interpretation. It has been read as fassalat (with a fatha on the fa and sad, light/unintensified), meaning it has separated between truth and falsehood. Ibn Zayd said: It separated between the Prophet—may Allah bless him and grant him peace—and those who opposed him, on the basis that fassala is a transitive verb, or that some of it separated from others through the variation of the pauses and meanings, on the basis that fassala is an intransitive verb meaning "it became separated," as in His saying: "When the caravan had separated" (12:94).

It has also been read as fussilat (with a damma on the fa and a kasra on the sad, light/unintensified), as a passive verb, and the meaning remains as previously mentioned.

"An Arabic Quran" – It is in the accusative case (nasb) due to praise, with the implied meaning of "I mean" or "I praise" or the like; or it is a state (hal). It has been said: [it is a state] from "a Book" because it is restricted by an adjective; and it is said: [it is a state] from "its verses." It is permissible for this state to be an emphasis for itself, or to be a preparation (tawti'ah) for a subsequent state. It is also said it is an accusative verbal noun (masdar), meaning "he recites it as a recitation." Al-Akhfash said: It is a second object (maf'ul thani) for fassalat, and this is as you can see, unless you happen to be Al-Akhfash.

In any case, the phrase "An Arabic Quran" conveys a sense of favor, as it is easy to recite and understand, having been revealed in the tongue of those among whom it was brought down.

"For a people who know" – meaning, who know its meanings because it is in their own tongue, assuming the object is deleted; or for the people of knowledge and contemplation, assuming the verb is treated as intransitive. The 'lam' in "for a people" (li-qawm) is for causation or specialization. They were specified as such because they are the ones who benefit from it. The prepositional phrase is either in the position of another adjective for "Quran," or it is linked to "revelation" (tanzil), or to "detailed" (fussilat).

Al-Zamakhshari said: It is not permissible for it to be an adjective like what preceded it and what followed it—meaning, "an Arabic Quran existing for an Arab people"—so that a separation is not created between the noun and the adjectives. Perhaps he meant to avoid the necessity of separating between the adjective, which is His saying, [the Exalted...]