Tafsir of Al-Baqarah 2:121

(Those to whom We have given the Book): This is a parenthetical clause to clarify the state of the believers among the People of the Book, following the mention of the states of their disbelievers. It is not conjoined [with the preceding verse] to draw attention to the complete disparity between the two groups. The verse was revealed regarding them, and they are the intended subjects of it—whether the relative pronoun refers to the entire genus or to a specific group—as it has been said that they are the forty who arrived from Abyssinia with Ja'far ibn Abi Talib; thirty-two of them were from Yemen, and eight were scholars from the Levant.

(They recite it with the right of its recitation): That is, they read it with the right of its reading, which is a reading that engages the entirety of the heart. In it, one observes the precision of the pronunciation, the contemplation of the meaning, and the due observation of the commandments and prohibitions.

The sentence is a "predestined state" (hal muqaddarah), meaning: "We gave them the Book, with their recitation being destined," because they were not reciting it at the exact moment of the giving. This is a qualifying state, for not everyone who is given the Book recites it.

"(Right/Haqq)" is in the accusative case as a masdar (infinitive) due to its annexation to the [following] masdar. It is also permitted that it acts as an adjective for an elided masdar, or as an accusative denoting state (hal), meaning: "reciting it while fulfilling its right."

The predicate is the statement of the Exalted: (Those are the ones who believe in it). It is also possible that (they recite it) is the predicate, not a state, and (those are...) is a second predicate or an independent, commencement sentence. Under the first two possibilities, the relative pronoun refers to the genus; under the latter, it refers to a specific covenant—that is, the believers among the People of the Book.

Advancing the subject (musnad ilayhi) before the verbal predicate indicates restriction and innuendo. The pronoun in (in it) refers to the Book—that is, those individuals believe in their Book, unlike the ones who distorted it, for they do not truly believe in it. From this, the benefit of the predication in the latter perspective becomes clear. You may also say the crux of the benefit is the gain attained from believing in it, as evidenced by what follows.

Some have interpreted the relative pronoun as referring to the Companions of the Messenger of Allah, may Allah bless him and grant him peace; this is the view of Ikrimah and Qatadah, and thus the "Book" here refers to the Quran. Others interpreted it as referring to the Prophets and Messengers, peace be upon them; this is the view of Ibn Kaysan, in which case the "Book" refers to the genus, encompassing the various scriptures. Others have stated what we have stated, but permitted the pronoun in (in it) to refer to "the guidance," or to the Prophet, may Allah bless him and grant him peace, or to Allah the Exalted. In both of those cases, the speech contains a shift (iltifat) from address to absence, or from first-person to third-person. The extreme remoteness of some of these interpretations is evident.

(And whoever disbelieves in it): That is, in the Book, due to distortion and disbelief in what confirms it. The potential references for this pronoun are also applicable here.

(Those are the losers): Because they traded belief for disbelief. It is also said: because of the trade they used to conduct by taking bribes to perform the distortions.