The editor tells us that if ever a private story were worth making public, then this is the one.
This man's life (that would be Robinson Crusoe's) is full of wonder and variety. It's also moral and can teach you a thing or two.
Also? The editor wants us to know that this tale is not fiction, but a "History of Fact." Its publication is a public service. (Pro tip: the novel is, of course, fiction. Defoe is just trying to amp up some sales.)