Bible scholars traditionally believe Mark is the earliest written Gospel, 66-74 CE. there is thought that at least one version existed before Marks, referred to as Q, which represents the German word Quelle, meaning ‘source’. They believe that Q and Mark informed the Gospels of Matthew & Luke. It is arguably the closest we will ever presently get to the earliest and therefore likeliest accurate text.
Background information on who Mark was can be found on the attached link, it is worth visiting, it is brief and succinct. If you do it is worth noting that scholars would dispute the notion that he is John Mark, an all too easy and convenient linking of a character mentioned in other New Testament sources. However, it helps set the scene for processing different points of view. It puts the reader on alert, that at every step an alternative view is possible or that someone will disagree. That Eisegesis, Is likely at every turn “an interpretation, that expresses the interpreter’s own ideas, bias, or the like, rather than the meaning of the text.”
The Gospel of Mark may have been considered an inferior abridgement of Matthew by Christian communities or if you are sceptical, it formed the basic structure on which information was added. I consider Mark as my primary Gospel or indeed New Testament source for information. When stories or accounts grow in detail over time, I feel they are less likely to be true. Additionally as Bart D Ehrman has indicated, the early Christian church was evolving and there were issues that writers, scribes, etc believed needed addressing, to preserve orthodoxy, significantly the growing need to establish Christ as a pre destined God, bound to die for our sins, be believed as a resurrected being and point us to eternal life through belief in him. The journey of thought, practice and belief between Mark and John is a leap from one side of a chasm to another, it defies my sense of logic and belief.