The Quran often retells earlier sacred history selectively, but selective is not the same as incomprehensible. Its aim is guidance, correction, and moral judgment, not to reproduce the Torah or rabbinic literature in full narrative form.

Why the objection has some force

The strongest version of the argument is this: the Quran mentions stories already known among Jews and Christians, sometimes without names, dates, or full plot. In the story of the two sons of Adam, it does not name Cain and Abel, does not describe the offerings in detail, and then connects the murder to a decree upon the Children of Israel. Critics say this only makes sense if the reader already has Genesis and later Jewish commentary in mind. They also point to verses telling people to ask "the people of the reminder," and to the use of Israiliyyat in tafsir, as evidence that Muslims themselves needed Jewish and Christian material to understand their book.

What the Quran is doing with earlier stories

And recite to them the story of Adam's two sons, in truth, when they both offered a sacrifice, and it was accepted from one of them but was not accepted from the other...

Quran 5:27

The passage is not unintelligible. Even without the names Cain and Abel, the reader can follow the essential lesson: envy, rejected piety, unjust murder, remorse, and the gravity of killing one soul. The Quran deliberately leaves out details that are not needed for its argument. This is one of its regular styles: it recalls known events, strips them to their moral core, and corrects how they are to be read.

The link to the Children of Israel is also not random. The first murder becomes the basis for teaching the sanctity of life to a later religious community:

Because of that, We decreed upon the Children of Israel that whoever kills a soul - unless for a soul or for corruption in the land - it is as if he had killed all mankind...

Quran 5:32

Yes, this resembles a statement found in Jewish tradition. That does not embarrass the Quranic claim. The Quran presents itself as confirming truths that remain from earlier revelation while correcting distortions, omissions, and false claims. Shared material is exactly what one would expect if the source of revelation is one.

Asking the people of scripture is not making them the judge

And We sent not before you except men to whom We revealed. So ask the people of the reminder if you do not know.

Quran 16:43; see also 21:7

In context, this verse answers those who denied that a human being could be a messenger. The instruction is simple: if you doubt that earlier messengers were human men, ask the people who possess earlier scriptural knowledge. It is not saying that the Bible is the final authority over the Quran, nor that every existing text and interpretation is pure.

The same applies to Quran 10:94, which speaks in a rhetorical and confirmatory style: those familiar with earlier revelation know that prophethood, revelation, and divine judgment are not new inventions. Classical scholars did not understand such verses as surrendering the Quran's authority to the Bible.

How Muslims treated Israiliyyat

Muslim scholars did cite Jewish and Christian reports, especially for names and background color. But they also set rules. Reports confirmed by the Quran and Sunnah may be accepted; reports contradicting them are rejected; reports about which revelation is silent are not used as creed or law.

Do not believe the People of the Book, nor disbelieve them, but say: We believe in Allah and what has been revealed to us.

Sahih al-Bukhari

Narrate from the Children of Israel, and there is no harm.

Sahih al-Bukhari

These two narrations together show the balance: limited permission, not dependence. Israiliyyat might explain who a person was said to be, or add narrative scenery, but the Quranic lesson stands without it.

So the objection establishes that the Quran speaks into a world where biblical memory was present, and that it sometimes assumes broad familiarity with earlier prophets. It does not establish that the Quran is incomprehensible, copied, or subordinate to corrupted texts. The Quran's claim is more precise: it confirms what is true, judges what is disputed, and gives the guidance needed for salvation.