(And those who disbelieved said...)

(And those who disbelieved) — and they are the polytheists of the Arabs — (We will never believe in this Quran nor in that which is before it). That is, from the ancient scriptures, as it is narrated from Qatada, as-Suddi, and Ibn Jurayj. Their intent is to negate belief in everything that points to the Resurrection from among the heavenly scriptures that contain it. It is narrated that the disbelievers of Mecca asked the People of the Book about the Messenger (may Allah bless him and grant him peace), and they informed them that they find his description in their scriptures, which angered them, so they said what they said. This is weakened by the fact that there is nothing in the preceding or succeeding context to indicate it. It has been said that "that which is before it" means the Resurrection.

Ibn Atiyyah categorized whoever said this as mistaken, on the grounds that "what is between the hands" in the language means what has preceded. This was critiqued by noting that it may be intended to mean what has passed, and it may also be intended to mean what is to come.

Yes, it weakens this view that "what is between the hands of a thing" is usually of its same kind. However, the substance of their statement in this regard is that they did not believe in the Quran nor in what points to it. As for the claim that it most commonly refers to what has passed, it has also been said that this is not universally accepted. At-Tabarsi recounted that the intended meaning of "those who disbelieved" is the Jews, and in that case, "that which is before it" would mean the Gospel. It is not hidden that this is a statement that should not be given any regard, and there is nothing in the context or the sequence to support it.

(And if you could see when the wrongdoers are detained before their Lord). The address is to the Prophet (may Allah bless him and grant him peace), or to anyone who happens upon it. The object of "see" is either "when" or is omitted; "when" is the adverb for it, meaning the state of the wrongdoers. "If" is for wishing, directed to other than the Exalted One; it has no answer, or the answer is implied, meaning: "You would have seen a horrific matter," or similar. "The wrongdoers" is an explicit noun placed in the position of a pronoun to register their state and clarify their deservingness [of this description]. The original meaning is: "And if you could see when they are detained before their Lord," meaning in the place of reckoning.

(They turn the speech back and forth among themselves). That is, they converse and debate one another. The sentence is in the position of a state. His saying, the Exalted: (Those who were oppressed will say), is an incipit (new sentence) to explain that debate, or it is a substitution for "they turn the speech back and forth" — meaning the followers say (to those who were arrogant) in the world, and led them into error and misguidance: (Had it not been for you, we would have been believers) in what the Messenger (may Allah bless him and grant him peace) brought.