In European/American scholarship the unknown material is referred to as "Q" (from the German 'Quelle,' for 'source'). "Inventor" is a strong word, as most modern scholarship agrees there are several other smaller sources that the gospel writers used. Some may have been novel, some allied with the writers, some independent but of the same faith. Of course there is some invention in all writing, even good writing.
Otherwise this is a fine overview of the literary quality of the gospels. It's helpful, in studying the gospels (and the rest of the Bible) to keep things in context. Although Luke explicitly states his is an "historical document" (I did a term paper on that conundrum in 9th grade), all four gospels are theology, not history. Each has his own discrete 'flavor;' Matthew is concerned with relationships to the Jewish community; Mark is drama/story; Luke connects Jesus to the Roman/pagan/commonfolk world; John, as you've noted, is 'higher' (more developed) theology and poetry.
I've studied the Christian Bible for 40 years, which doesn't make me an expert. It only means I know what I'm reading, and its provenance. That gives one a lot of useless information, much of which would be corrosive to the typical parishioner's faith. I try to proceed on the basis that I don't go to Newton, Sagan or Hawking (or UM) to buttress my faith, and scripture isn't intended to give us scientific, astronomical or historical information (but the gospels aren't bad on sociology of the time and local geography). It's not even a matter of scripture being the "comic book" version of the "classics" in history or any other endeavor. They are unique documents, each giving a different perspective on Jesus, making no apologies that their four accounts are not consistent, but are complementary.
Edited by szentgyorgy, 04 July 2013 - 03:42 PM.