It’s rather obvious, the lesson.  A so-so novel.  But too many Americans (how about we start with Dick Cheney) have not been able to absorb the one lesson of modesty and humility woven through the fabric of the novel.  Unbeknownst to Greene, and an infinite jest at that, the novel stands the test of time after 60 years in terms of its idea, if not in terms of its writing.