This verse is the "Closing Argument" of the most detailed narrative in the Quran.
By claiming to be a "detailed explanation" and a "confirmation," the Quran effectively locks its own validity to the historical and textual accuracy of the very books it is supposed to be "explaining."
Surah 12:111:
There was certainly in their stories a lesson for those of understanding. Never was it a narrated invention, but a confirmation of what was before it and a detailed explanation of all things and guidance and mercy for a people who believe.
If I give you a "detailed explanation" of the US Constitution, but I tell you that the Constitution says the US is a Monarchy, my explanation is a failure.
The Quran claims to be a "detailed explanation" of the previous Scripture. However, the previous Scripture (the Bible) is built on the foundation of the Covenant of Blood and the sacrificial system.
If the Quran "explains" the Bible but removes the Blood Atonement, it has failed its own definition of Tafṣīl. It hasn't explained "all things"; it has deleted the main thing.
Since 12:111 ends the story of Joseph, the polemicist looks at the "confirmation."
The Bible’s account of Joseph (Genesis 37-50) ends with Joseph’s specific prophecy about the Exodus and the bones of the patriarchs being carried out of Egypt—affirming the unique Covenant with Israel.
The Quranic version omits the specific covenantal promises that make Joseph’s story meaningful in the context of salvation history.
If the Quran is a "confirmation," why does it strip the story of its biblical "Guidance and Mercy" regarding the promise to Abraham, Isaac, and Jacob?
The verse says the lessons are for "those of understanding" (li-ulī al-albāb).
A "man of understanding" is someone who can compare two documents and spot a discrepancy.
When a Christian "of understanding" compares the Bible (the book "between the hands") with the Quran (the "explanation"), they find a total theological mismatch.
According to 12:111, the Quran's purpose is to confirm the Bible. If a "man of understanding" finds that the Quran contradicts the Bible, then he is forced—by the logic of this very verse—to reject the Quran to remain faithful to the "confirmed" Scripture.
Since this verse claims the Quran is a "detailed explanation of all things," how do you think Christians react when they find the "detailed explanation" of the Trinity is something the Quran condemns but never actually "explains" it correctly!?