Why not combine Matthew, Mark, Luke and John into one Gospel?
Why does the New Testament have four Gospels? After all, they all tell the same overall story: the life, death, and resurrection of Jesus. So why not just collect up all the stories about Jesus and harmonize them as the “Unified Story of Jesus”?
The answer is quite complicated. In principle, you could imagine cutting out every story about Jesus from Matthew, Mark, Luke, and John, and then pasting them back in some order that you would have to decide.
Some “stories of Jesus” are repeats
Some questions could be decided fairly easily. For example, what to do about stories that occur multiple times? An example is the baptism of Jesus, which appears in Matthew, Mark, and Luke. Matthew’s version has slightly more detail. You might decide to choose the most detailed version in cases like that.
The Resurrection of Jesus is a more complicated example of this sort. All four Gospel writers record that women were the first people to witness the event. One of whom was Mary Magdalene. All the accounts reveal that the tomb was open when the women arrived. Matthew provides the additional detail of an earthquake. Two angels (one in Matthew) tell the women what happened. In Matthew and Mark, the angel(s) instruct the women to tell the disciples to meet Jesus in Galilee. Luke reports that the disciples rejected the news as an ‘idle tale’. John’s is the most extensive, and most beloved, account. It’s where Mary meets the Risen Christ in person but at first mistakes him for a gardener.
But sometimes the Gospel writers disagree
There are also occasions when the Gospel writers disagree. For examples, the Annunciation of Jesus’ birth. In Matthew, an angel tells Joseph that his engaged wife Mary will have a son and that he, Joseph, should name him Jesus. In Luke’s Annunciation narrative, the angel appears to Mary. There is no mention Joseph at all. It would be difficult to harmonize these accounts.
The accounts of the crucifixion differ in so many details that to merge them would make the overall account rather opaque. Some of the details even contradict one another. An important example concerns Jesus’ last words. Matthew and Mark record them as, “My God, why have you forsaken me?” In Luke, they are, “Father, into your hands I commend my spirit.” John tells something else again, “It is finished.”
All agree that Jesus was the Son of God
Their “agenda” of all four Gospel writers was that we, the readers, should believe that Jesus was the Son of God. John even states this explicitly [John 20: 30]. In their day, the term “Christian” did not yet exist, so for the Gospel writers, the Son of God was the Jewish Messiah. This quasi-divine figure was expected to bring about God’s Kingdom of righteous rule.
However, who was that Son of God? The Gospel writers differed considerably in their answers. That is the most difficult obstacle to a unified Gospel.
Mark describes the most human and least spiritualized Jesus. Some early Christians even believed that God “adopted” an ordinary man as his Son at the moment of his baptism. Jesus carried out his ministry as the Messiah until he was crucified. Then God released him from his role as Messiah when he cried out, “My God, why have you forsaken me?”
At the other end of the spectrum, John imagined a very spiritual, divine Jesus. He explained this in the very beginning of his Gospel. “In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God.” Jesus, the Word (Greek, logos) was part of the divine essence even before time began.
Christology: what was the relationship between Jesus and God?
We use the word ‘christology’ to describe Jesus’ divinity. Mark has a low christology, John a high christology. Matthew and Luke are in between. Among the doctrines of modern Christians, we might say that Roman Catholicism and Eastern Orthodox represents high christology. Conversely, that many Reform evangelicals subscribe to a low christology.
The Gospels came into being when the early “Christians” were trying to figure out the meaning of the life, death, and resurrection of Jesus, the Son of God. Scholars assume that each Gospel was the creation of a specific early Christian community. Each community would have had its own stories about Jesus, and its own interpretations of them.
To sum up
In my opinion, to try to conflate the four Gospels would destroy their distinctive flavours (that is, christologies). It would take away from the richness of the tapestry rather than bring out the many colours of the whole.