If one is to look at the five chapters of the book and derive one lesson from each one, the five lessons might look something like the following:
Chapter 1: It is clear that there are always going to be obstacles to helping the poor and disadvantaged, at times there will even be other people that one must fight in order to help the poor.
Chapter 2: The rules are not always made to benefit everyone, and sometimes they ought to be broken in order to help people.
Chapter 3: Dr. Farmer believes that he must do anything necessary to treat people and that if they don't get better, it is his fault. He doesn't want to depend on medicine or the regular western practice of it, he just wants to cure people.
Chapter 4: Farmer always insisted that he had to see people first hand in order to understand how to treat them
Chapter 5: Perhaps a lesson that can be learned is that success can come from unexpected sources and methods, that part of Farmer's success comes from his willingness to think outside the box at times.