This is a Meccan surah revealed during a time of intense persecution for the early Muslims. These verse provides the mandate for how Muslims are to interact with Christians and Jews, grounding that interaction in a shared belief in the same God and the same revelation. The Quran is the same "type" of revelation as the Bible, the people who possess the Bible will naturally recognize and believe in it.
Surah 29:46-47:
And argue not with the People of the Scripture unless it be in (a way) that is better, save with such of them as do wrong; and say: We believe in that which hath been revealed unto us and revealed unto you; our Allah and your Allah is One, and unto Him we surrender. In like manner We have revealed unto thee the Scripture, and those unto whom We gave the Scripture aforetime will believe therein; and of these (also) there are some who believe therein. And none deny Our revelations save the disbelievers.
In verse 46, Muslims are commanded to say they believe in what was "revealed unto you" (to the Christians).
You cannot be commanded to "believe" in a corruption or a lie. By telling Muslims to affirm the revelation in the hands of the 7th-century People of the Book, the Quran is certifying the integrity of the Bible at that time.
If the Bible was uncorrupted in the 7th century, then its teachings on the Trinity and the Cross are true. If those teachings are true, the Quran (which denies them) is false.
The verse claims "Our God and your God is One."
If it is the same God, He cannot contradict Himself on His own nature.
The God of the Bible ("Your God") says He is a Father who sent His Son to die. The God of the Quran ("Our God") says He has no son and no one died on the cross.
If they are the same God, one of these descriptions is a fabrication. Since the Quran affirms the Biblical revelation as coming from this "One God," it has no grounds to claim the Bible's description of that God is a "corruption."
Verse 47 claims that those who were given the Scripture "will believe" in the Quran.
This is a testable, historical claim. If the Quran truly matched the "Scriptures of old," the Jewish and Christian scholars would have flocked to it.
The overwhelming majority of the Ahl al-Kitab rejected the Quran precisely because it contradicted the Scripture they held. Verse 47 essentially says: "If you know the Bible, you'll know this is true." When Christians say, "We know the Bible, and this is NOT true," they are following the Quran's own logic to its conclusion.
Surah 29:46 tells you to say to me: 'We believe in what was revealed to you.'
What was revealed to me—and what we have in our manuscripts from that era—is the Gospel of Jesus Christ. It says Jesus is the Son of God. Do you believe that?
If you say the Bible is corrupted, then you are disobeying the command of 29:46, which tells you to affirm what was revealed to us.
Verse 47 says that those who have the Scripture 'will believe' in the Quran. I have the Scripture, and I see that the Quran contradicts the fundamental message of the Prophets.
According to your own Book, if I am a follower of the 'Remembrance' and I don't see the Quran in my Book, then the Quran has failed the very test it set for itself.
Either your God and my God are different (making the Quran false), OR the Quran's claim that we 'will believe' is a failed prophecy."
Why the "One God" tell the Christians one thing for 600 years and then tell Muhammad the exact opposite? The historical reality was massive rejection by the People of the Book.