This verse provides a specific historical timeline for the presence and reliability of the Jewish scriptures. It eliminates the argument that the Bible was corrupted centuries before Muhammad.
Surah 2:89:
"And when there cometh unto them a Scripture from Allah, confirming that in their possession—though before that they were asking for a signal of triumph over those who disbelieved—when there cometh unto them that which they know (to be the truth) they disbelieve therein. The curse of Allah is on disbelievers."
The phrase "lima ma'ahum" ("that which is with them") is the most devastating part of this verse for Islam.
If the Quran came to confirm what was "with them" in 622 AD, it was confirming the Torah manuscripts currently in the synagogues of Medina.
We have today the Dead Sea Scrolls (pre-Christian), the Septuagint, and the Masoretic tradition. These prove that the Torah in the 7th century was identical to the Torah we have today.
If the Quran confirms the 7th-century Torah, it confirms a book that denies Muhammad's prophethood and outlines a sacrificial system fulfilled in Christ.
The verse claims the Jews recognized the truth because of what they already had (ma 'arafū).
You cannot "recognize" a person you’ve never seen, and you cannot "recognize" a truth if your source book is a corrupted mess.
If the Jews were able to recognize the truth of a revelation based on their current scriptures, those scriptures must have been a perfectly clear and reliable mirror of God's Word.
If they were reliable then, and we have the same books now, then the Torah remains the ultimate standard of truth.
The verse mentions the Jews were "asking for a signal of triumph" (praying for the Messiah/Prophet) based on their books.
The Jews were looking for a Prophet because their scriptures told them to.
If their scriptures were corrupted, their expectation of a prophet would be based on a lie. But the Quran affirms their expectation was valid; it simply says they rejected the "fulfillment." Therefore, the book that created the expectation must be the uncorrupted Word of God.
In Surah 2:89, the Quran says it came to confirm the book that was 'with' the Jews in the 7th century CE. We have the manuscripts from that exact era. They are the same as our modern Bibles.