Your essay will be stronger if you write your thesis yourself, but here are some ideas:
You may want to write a thesis that states that Steinbeck's 'The Pearl" is a parable (or fable, if you wish) of how individuals relate to the world. Your three points could show the main ways in which Kino's relation to the world changes.
Of course, his finding of the Pearl of the World alters the attitudes of others, but his attitude also changes greatly. For instance, when it is suggested that he be rid of the pearl, Kino declares, "The pearl has become my soul...If I give it up I shall lose my soul." However, the greater evil seems to be his greed and holding onto the pearl without offering to share any of the wealth as well as his becoming a target of hit men.
Check out the questions and answers on this book as well as the discussion group; two good links are listed below that may help.