OK, I think we've taken this far enough. Let's get back to our text.
No, wait. I just can't let it go without one more comment, albeit one that is somewhat tongue-in-cheek.
You mentioned that Luke's version of Matthew's Sermon on the Mount is called the Sermon on the Plain. Even if we were to allow that people hear what they want to hear, and that this explains the differences between Matthew and Luke (something I cannot fully accept), still it strikes me as odd that the people listening to Jesus couldn't remember if they were standing on a mountain or a plain. Talk about not paying attention!
All right. Enough. Please lead us to the next Beatitude before I start babbling on about how Paul wrote long before any of the Gospel writers and that since he mentions almost nothing of the Jesus narrative (Virgin Birth, parables, Sermon on the Something, etc.) there is a case to be made that these were all narrative flourishes of great writers.
I love the Bible— the Hebrew Bible, the Apocrypha, and the New Testament— and one of the reasons I love it is because it is great fiction, and like all great fiction it is at times deeply and powerfully true. I have no more problem with the differences between biblical texts than I do with differences among Shakespeare's plays. And just as the truth found in Shakespeare has nothing to do with the historicity of his plays, so the truth of the Bible has, for me, nothing to do with historicity of the stories. The story's the thing. Let's get back to it.