Tafsir of Al-A'raf 7:170

{And those who hold fast to the Book}: That is, they adhere to it in the matters of their religion. It is said: Masaka bi-al-shay’ and tamassaka bihi carry the same meaning. Mujahid and Ibn Zayd said: They are those who believed among the People of the Book, such as Abdullah ibn Salam and his companions, who held fast to the Book that Moses, peace be upon him, brought, and they did not distort it, nor did they conceal it, nor did they use it for gain. ‘Ata’ said: They are the nation of Muhammad, may Allah exalt his mention, and the intent by "the Book" is the Glorious Quran.

Abu Bakr and Hammad recited it as Yumsikuna (with the light shad), derived from al-imsak (to hold). Ibn Mas’ud recited it as Istamsaku, and Ubayy recited it as Masaku. This is in agreement with His saying: {And they establish prayer}. The change in the famous recitation is intended to indicate that adherence is a continuous affair across all times, unlike establishment (of prayer), which is specific to designated times. Specifying it [prayer] for mention among all other acts of worship—even though it is included within the adherence to the Book—is due to its superiority over them, as it is the pillar of religion.

The grammatical position of the connective al-mawsul ("And those...") is either in the genitive case, as a conjunction to {those who fear [Allah]}, and His saying: {Do you not then use your reason?} is a parenthetical clause confirming what preceded it. A parenthetical clause may be linked with the particle fa, as in the saying: Fa-i’lam, fa-‘ilmu al-mar’i yanfa’uhu... ("Know, for the knowledge of a man benefits him..."). Or, it is in the nominative case, as the subject, with the predicate being His saying: {Indeed, We do not allow the reward of the reformers to be lost}.

The connector [linking the predicate to the subject] is either an omitted pronoun, as is the opinion of the majority of the Basrans—meaning: the reward of the reformers among them—or it is the definite article (al) as per the opinion of the Kufans, for it acts as a substitute for the pronoun, as if it were said: "their reformers." As for the generality implied by "the reformers," it is considered one of the common connectors, similar to Ni'ma al-rajulu Zayd ("Excellent is the man, Zayd") according to one of the interpretive views. Alternatively, the explicit noun was placed in the position of the pronoun on the basis that the original was "We do not allow their reward to be lost," but it was altered for the aforementioned reason to alert that righteousness (salah) acts as a preventative against loss; for linking a ruling to a derivative [attribute] signifies that the basis of the derivation is the cause, as if it were said: "We do not allow their reward to be lost because of their righteousness."

It is also said: The predicate is omitted, and the estimation is: "And those who hold fast to the Book are rewarded or recompensed." In this case, His saying: {Indeed, We do not allow...} is a parenthetical clause confirming what preceded it.