 But under Marcan posteriority, Mark must have added these many details to make his stories more vivid and clear.In either case, Mark must have had an independent source (traditionally, Peter) spanning nearly his entire Gospel; but if so, Marcan posteriority requires a complex and skillful weaving together of this source with both Matthew and Luke, even within individual sentences, which would have been a challenging task.Often the differences in Mark from the parallels in Matthew and Luke are "hard readings" (Lectio Difficilior), which seem to portray Jesus or the apostles in a negative light or in ways that a later redactor would likely find uncongenial.