I sought to answer this question in a column that came out on April 21 but let me try again.

Mark 14:50 is insulting to the disciples in that it portrays them as weak and cowardly. By the time the earliest gospel, Mark, was written, some 40 years had passed since the event of the crucifixion. The disciples were now viewed as heroes. The tendency of history is to whitewash and exaggerate the goodness of heroes. The fact that the detail of apostolic desertion was not omitted makes it ring with authenticity.

Second, this desertion is explained by an appeal to the scriptures of the Jews. That is, an elaborate defense of this apostolic desertion is given a biblical basis on five occasions in the gospels. That defense appeals primarily to a verse in Zechariah (13:7) that says when the shepherd is struck, the sheep will be scattered. The gospel argument attempts to exonerate the disciples in their desertion by saying, "they had to act in accordance with the scriptures. The scriptures had to be fulfilled." When you explain why heroes did not act heroically, you seem to be affirming the historicity of the act you are explaining.

That is just one of the clues that scholars use when they are trying to make historical judgments about any part of the gospel tradition.

-- John Shelby Spong