Dan Everett originally moved to live with the Piraha, a remote Amazonian tribe situated in central Brazil, to try to convert them to Christianity. He eventually spent 30 years with them, learning their language and studying their culture. In the end he gained profound insight into their society but lost his faith and many of his friends and family in the process.
This book is divided into three sections - the first contains Everett's observations as to how the Piraha live, their world view, customs etc. This is the most interesting section. For example, the Piraha don't have words for colour! Nor do they have a number system or a creation myth and they don't talk about or believe in anything that occurs outside of their direct experience (this includes abstract concepts like numbers, colours). And it so happens that the Piraha are some of the happiest people Everett has encountered in his wide travels!
Everett postulates that because the Piraha are not culturally conditioned to concern themselves much with the past or future and also because they are culturally conservative and do not crave the experiences and objects of other cultures and also because they are so naturally confident in their their ability to survive in the jungle, they do not suffer from the worry and existential crises that plague other societies.
Ultimately Everett found religion to be nothing but "elegant theorizing" - a desire for humans to simplify their experience. The Piraha are pragmatic; they are happy without absolute truths. God for them is living, breathing, dying. Ultimately, don't you think that's all there is? And that there could be freedom in just that? I think so. I agree with Everett absolutely.
I found the section on linguistics a bit too technical for my liking but if you skim it (like I did) you'll still find much food for thought. Be prepared firstly to have your assumptions about so-called "primitive" societies vs. "advanced" societies mightily challenged.
Don't Sleep, There Are Snakes: Life and Language in the Amazonian Jungle/ Daniel L. Everett / Pantheon Books / PB, 2009