I am sometimes asked if there is only one Injil then why are there four Gospel books in al Kitab (the Bible), each written by a different human author? Would that not 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. And on this point the Qur’an is in full agreement as we saw in the post on 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 would testify about the Injil.
But how to understand the four Gospel books for the one Injil? In the Qur’an there are often several passages that recount one event, and taken together allow us to have a fuller picture of that event. For example, the scriptures for the Sign of Adam used Surat 7:19-26 (The Heights) to tell us about Adam in Paradise. But it also used Surat 20: 121-123 (Ta Ha). And this 2nd passage gave an extra understanding of Adam by explaining that he was ‘seduced’, which The Heights does not include. Taken together they gave us a more complete picture of what happened. That was the intent – to have the passages complement each other.
In the same way, 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.
This is why when the content of the Injil is talked about it is always in the singular, because there is only one Injil. For example we see here in the New Testament that there is one single gospel.
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 Gospel is also written in singular in the Holy Qur’an (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 required a minimum of ‘two or three witnesses’ (Deuteronomy 19:15) to testify about the one particular event or message of interest. By providing four witness accounts the Injil is supported above the minimum requirements of the Law.