Sentence:  "Should they live and build their church in the American wilderness, their worst dangers would rise in and among themselves rather than outside. That was the <WSD>gist</WSD> of the lesson from their pastor and "wellwiller" John Robinson." 
Meaning of the word marked with <WSD> tags:  The most essential part; the main idea or substance (of a longer or more complicated matter); the crux of a matter; the pith.