Gospel unity
John should not be separated out from the other gospels. It is the 4th snapshot of doctrine being taught in the Hebrew church, given to the Gentile church.
Mark wrote the testimony of Peter. It was the first snapshot taken early in the church. The men on the road to Emmaus had returned astonished at the teaching of Jesus in his resurrection. It was the same teaching they had received before the cross, but now their eyes were opened. Everything in the scriptures spoke of Christ. They could not reproduce what they had heard, but now they had seen the lid on the jigsaw puzzle to know what to look for.
The disciples had been given the Holy Spirit to remind them of what they were taught and lead them in truth. As they read the scriptures, the mystery began to make sense. The Spirit did not give them instant knowledge as if it were a taste of omniscience; they learned to study and search scripture properly setting the foundation for teaching.
Each author had access to the earlier texts. He had reasons based on further study to make the changes. Matthew and Luke intentionally revised the earlier works to improve the teaching. They had an opinion on what and how to relate their interpretation of the Old Testament in light of what they were reminded of the life of Christ. Christ fulfilled scripture in many ways. The Old Testament has many layers of meaning having pericopes within pericopes and layers on layers. The differences between the gospels reflect the hermeneutic tools they were using at the time of the snapshot.
The Gentile church did not use the Old Testament in Hebrew. They could not unpack the mystery from the Septuagint. Mark was used to give them a deeper insight. The book did not stand alone. It was delivered to the Gentile church by messengers who used the text as an outline to teach. The messengers understood much more from the Hebrew OT than contained in the book, and added those insights when teaching from the book.
Peter's insights into the mystery were limited but he began the work, often making the point that the actions and teachings of Jesus fulfilled prophecy. His attempt to teach in the language of mystery failed. He taught that we can handle snakes and drink poison; and we can IF we understand what it says in riddle. We will withstand temptation, and learn things (as from University) that are harmful, but will not be hurt by either. Those who read his teaching literally were put in harms way, so some churches removed that teaching from the book of Mark.
Ten or fifteen years later, the Hebrew apostles had learned more and had more hermeneutical tools available to unpack the mystery. Matthew was aware of Mark's work since it was being used everywhere as New Testament writing. It is likely that James wrote sometime during this period making sure people understood that the serpent was just a symbol of the temptation of your own heart, and correcting the misunderstanding of the end of Mark.
Peter/Mark understood the beginning of the story to be the preaching of John the Baptist. As he related the life of Christ as the fulfillment of scripture he used his life beginning with the testimony of John. When Matthew wrote, the Hebrew church had discovered that Israel in scripture, was a parable to the nations. Matthew saw things in the history beginning with Abraham that were fulfilled in Christ.
Another decade had passed when Luke began to write. By then the apostles discovered that the lives of the men prior to Abraham also were a parable of Christ. Luke began his telling of the life of Christ with Adam. The church realized that the interpretation of the mystery in the Old Testament was dependent upon a recollection of the actual life of Christ. Before all the eye-witnesses died, Luke attempted to capture their memories and with this purpose, interviewed many. He had both the books of Mark and Matthew available. With each book, the audience was more and more Gentile and Greek. They had less foundational knowledge of the scriptures.
This Greek church became arrogant and began separating from the Hebrew church. John himself was unable to visit a church being disallowed by a Greek church ruler. How much power did this man have that John could not even visit the city and talk to old friends? How antagonistic to the Hebrew scriptures had they become? It is likely that so many Judaisers had wreaked havok attempting to get everyone to be circumcised, that the ruler just wanted no more Jews.
All the apostles but two were dead, and Peter asked John to write a book explaining the mystery so it would not be lost. There were three editions of the "Life of Christ" in circulation and John had no need to use most of that material. He had become proficient with notarikon, the attribute of the Hebrew language where words get their meaning from the combined meaning of the letters. His book could be called "The life of God on earth" seeing more than the literal life of Christ. He began with Gen 1:1 obtaining John 1:1-4 from the first three words.
Now a flashback to Paul. He was called early to be the missionary to the Gentiles and they flooded in. The apostles were reminded of what Jesus taught them of his death and resurrection, and were busy searching the scriptures for those prophecies. What they missed were they prophecies of the bride. They did not understand the invasion of the Gentiles. Jesus taught Paul of the bride after his resurrection. As Paul read scripture, he did not so much look for the cross as use the cross as a pointer to the bride.
This confuses modern theologians; many thinking that Paul has a different gospel than the others. It is not different in the least but is directed at the life of the bride in Christ as taught in the mystery, rather than merely the life, death and resurrection of Jesus in the mystery. The others worked from their memory of Christ to see him in scripture. Paul worked from scripture to see Christ and his bride.
John is not a separate entity, but the latest snapshot from the Hebrew church on the state of theological understanding derived from the mystery. The four Gospels are a record of the Hebrew church reproducing the sermon on the road to Emmaus.
For any other gospel to fit into this record it would have to be written by eye-witnesses to the life of Christ, since it is his life that is used to unpack the Old Testament scriptures. It's purpose must be to recapitulate the OT mystery through the life of Christ. It must have evidence in starting within the Hebrew church and being passed to the Gentile church. And it must have evidence that the Gentile church received it as authoritative, both using it and passing it on.
