Let me state this as clearly as I can…
(I’ve picked up something of Scot McKnight’s combative tone of voice here.)
The sermon on the mount in Matthew 5-7 was not preached to or for the benefit of the post-Christendom, modern-going-on-postmodern, global church.
It was preached to beleaguered first century Israel. It was a call to a section of first century Israel to pursue a particular course of action, to think in a particular fashion, to embark on a particular journey at a time of extreme national crisis, when a storm and a flood were about to sweep away the house that Israel had built on the sand.