6:57 PM Mark as an enabling document:
Matthew is the fundamental Gospel and the most important, but each was written and published in response to a particular need of the church in a particular historical situation. The real significance of Mark lies in Peter’s guarantee that Luke was fit to be read beside Matthew in the churches of both Peter and Paul. Mark is therefore to be viewed as the bridge between Matthew and Luke, that is, as a document enabling Luke’s Gospel to be used freely in all the churches to which the authority of Peter, the chief eyewitness, extended; and it stands as a recognition of the equality of the Gentiles in all the churches.
From Why Four Gospels?