Mark’s Gospel is the founding document of the united Christian church; it was classified as canonical
from the very start. In addition, the leaders of the three individual churches, James, John and Peter, are presented jointly in Mark’s Gospel as witnesses to the core statements of faith of all three single churches.
The core statements of faith are:
1. Mark 5:37, Jairus’ daughter: resurrection (John’s church)
2. Mark 9:2, transfiguration: glorification (Peter’s church)
3. Mark 14:33, Gethsemane: suffering (James’ church).
In other words, each individual church also confirmed the core truths of the faith of the other two churches.
Mark on the status of his Gospel writings as canonical:
In the story of the transfiguration, Peter wants to build three huts (= three temples, three churches) (v. 5), attesting to the three individual Palestinian churches from which early Christianity emerged.
But the narrator Mark corrects him: the three individual churches are history; their authority in matters of faith has passed on to the evangelist, who preaches the Gospel of the whole church (v. 6: (Peter) did not know what to say, they were so frightened.).
Mark’s Gospel also deals with the Jewish defeat in the revolt against the Romans in 70 AD. Why? Homer’s Iliad ends with the death of Hector, the Trojan hero, pointing to the fall of Troy. In the same way Mark’s Gospel ends with the death of Jesus, the Jewish hero, that points to the fall of Jerusalem.