Many Muslims make objections to the Christian faith in the form of accusations against the reliability, preservation, and trustworthiness of the Bible. There are all sorts of arguments for the tenacity of the biblical text: its historical reliability, trustworthiness, and verisimilitude. However, when it comes to Muslims in particular I think a very cogent argument can be made that the Qur’an itself argues for the preservation of the Christian scriptures. The following is what I routinely present to Muslims as an argument commonly referred to as the Qur'anic Conundrum:
1. The Qur'an routinely refers to the "previous Scriptures," identified as the "Torah" (توراة - Tawrat, mentioned 18 times) and the "Gospel" (إنجيل - Injil, mentioned 12 times). These books are prefaced with the descriptors of being "sent down by God," as seen in places like Surah Ali 'Imran 3:3 and Surah Al Ma'iadh 5:68: :
"He has sent down upon you, [O Muhammad], the Book in truth, confirming what was before it. And He revealed the Torah and the Gospel;"
"Say, "O People of the Scripture, you are [standing] on nothing until you uphold [the law of] the Torah, the Gospel, and what has been revealed to you from your Lord." And that which has been revealed to you from your Lord will surely increase many of them in transgression and disbelief. So do not grieve over the disbelieving people."
2. Muhammad is told by Allah in Surah Yunas 10:94, that if he has doubt he should look to the Jews and the Christians because they have the previous Scriptures:
"So if you are in doubt, [O Muhammad], about that which We have revealed to you, then ask those who have been reading the Scripture before you. The truth has certainly come to you from your Lord, so never be among the doubters."
3. In context to mentioning the previous Scriptures the Qur'an declares that Allah's words cannot be changed in Surah Al-An'am 6:114-115:
"[Say], "Then is it other than Allah I should seek as judge while it is He who has revealed to you the Book explained in detail?" And those to whom We [previously] gave the Scripture know that it is sent down from your Lord in truth, so never be among the doubters. And the word of your Lord has been fulfilled in truth and in justice. None can alter His words, and He is the Hearing, the Knowing."
4. Christians in Surah Al-Ma'idah 5:46-47 are told to judge by the Gospel and if they do not do so they are "defiantly disobedient":
“And we sent, following in their footsteps, Jesus, the son of Mary, confirming that which came before him in the Torah; and We gave him the Gospel, in which was guidance and light and confirming that which preceded it of the Torah as guidance and instruction for the righteous.
And let the People of the Gospel judge by what Allah has revealed therein. And whoever does not judge by what Allah has revealed - then it is those who are the defiantly disobedient.”
Conclusion: If the previous Scriptures sit in a chain of succession (as is alluded to by verses like 4:46) then it makes logical sense that you cannot remove one of the links of the chain without compromising the others. If indeed the Torah and the Gospel are corrupt, as modern day Muslims would have us believe, then the author of the Qur'an seems to have no knowledge of it. In fact, there is evidence to the contrary that the author of the Qur'an actually articulates their trustworthiness and authenticity as God's word.
Similarly, if the Gospel and Torah are God's word and no one can change God's word then how have these previous Scriptures become corrupted? Did Allah not know they would be corrupted - in which case he is not all-knowing? Could he not stop individuals from doing so - in which case he is not all powerful? Or is what we have in Surah 6:115 incorrect, in which case the Qur'an itself has been compromised?
In conjunction with accusations of change, why would Muhammad be encouraged to talk to a people who had corrupt Scriptures in 10:94? Would this not only confuse Muhammad as there are clear teachings being revealed to him for the Qur'an that inherently contradict what is in the Torah and Gospel?
We know exactly what "the Torah" and "the Gospel(s)" looked like during the late 5th and early 6th centuries of Muhammad's lifetime. We even have manuscripts from the areas near Syria and the Arabian peninsula from this specific time period. They are virtually identical to the modern Gospels and Torahs we have in translation today. Thus, if these commands had any application for their original audience then what was "the Gospel" and "the Torah" being discussed in Surah 10:94? If we know what these documents looked like in the time period that these verses have application then the evidence shows no serious difference from what we have today.
Finally, why would Allah tell Christians to judge by the Gospel if it had been corrupted? If the Torah and Gospel the Qur'an is continually talking about are not the Torah and Gospel(s) we have today then how is the eternal revelation of the Qur'an to speak to modern day Christians? Why bother making the statement that Christians are to "judge by what Allah has revealed therein" lest they be "the defiantly disobedient?" Why not simply tell the Christians outright that these former revelations were corrupt and to get rid of them in place of the more perfect Qur'an?
If I take the Qur'an at its word as a "person of the Gospel" and I judge the Qur'an by the Gospel that has been revealed to me, in accordance with the command in Surah 5:47, I find it wanting. I see no interaction with any of the discussions taking pace in the Gospel nor any indication regarding knowledge of what Jesus is recorded saying there. In fact, what I do see are continual contradictions and misunderstandings regarding what the Gospel says and teaches and therefore, if the Qur'an is true and I obey its command to me then I have to conclude that it is false.