If there is only one Injil then why are there four Gospel books in al Kitab (the Bible)? Matthew, Mark, Luke and John are each written by a different human author. Would that make them of fallible (and contradictory) human origin and not from Allah?
The Bible (al Kitab) says about itself:
“All scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness, so that the man of God may be thoroughly equipped for every good work”.2 Timothy 3:16-17
So the Bible/al Kitab makes the claim that God is the final author since He inspired these human authors. On this point the Qur’an is in full agreement as we saw in what the Qur’an says about the Bible. We also saw here that Isa al Masih promised his disciples guidance from the Spirit of Truth when they wrote the Injil.
Adam in Quran: One Adam but Two Surahs
But how to understand the four Gospel books for the one Injil? The Qur’an sometimes has several passages that recount one event. Taken together these surahs allow us to have a fuller picture of that event. For example, the Sign of Adam referenced Surah 7:19-26 (The Heights) to tell us about Adam in Paradise. But it also used Surah 20: 121-123 (Ta Ha). Surah Ta Ha gave extra information about Adam when explaining that he was ‘seduced’. The Heights Surah does not include this. Taken together they gave us a more complete picture of what happened. That was the intent – to have the passages complement each other.
Similarly, the four Gospel accounts in the Bible (al Kitab) has always and only been about one Injil. Taken together they give a fuller understanding of the Injil of Isa al Masih PBUH. Each of the four accounts has some material that the other three do not. Therefore, taken together, they offer a more complete picture of the Injil.
So when we discuss the content of the Injil we always refer to it in the singular. This is because there is only one Injil. For example we see that the New Testament refers to one single gospel (by using pronouns ‘the’ and ‘it’).
I want you to know, brothers, that the gospel I preached is not something that man made up. I did not receive it from any man, nor was I taught it; rather, I received it by revelation from Jesus Christ.Galatians 1:11-13
The Holy Qur’an also refers to the Gospel in the singular in (see The pattern of ‘Gospel’ in the Qur’an). But when we speak of the witnesses or the books of the gospel there are four. In fact, in the Taurat, a matter could not be decided by the testimony of only one witness. The Law of Musa PBUH required a minimum of ‘two or three witnesses’ for legal decisions.
One witness is not enough to convict anyone accused of any crime or offense they may have committed. A matter must be established by the testimony of two or three witnesses.Deuteronomy 19:15
By providing four witness accounts the Injil exceeded the minimum requirements of the Law.