The Economist sorts out the small differences in the four gospels:
Matthew speaks of a lamp giving light to “all those in the house”; Luke speaks of a lamp to guide “those coming into the house”. For Martin Dibelius, a German scholar, that was one clue—among many—that the material collected by Matthew was prepared for a Hebrew public, who were in a sense already illuminated; Luke’s words were aimed at “Gentile” newcomers. Dibelius reckoned the Gospels were collections of mini-sermons, collated rather than written by the Gospel authors; and he tried to work out who the target audiences had been.
The Dish 