In his novel/autobiography, Black Boy, Richard Wright writes of how his reading took him to other environments and taught him greatly about the world. Certainly, literature teaches moral truths to the reader, truths that the reader can apply to his/her life, truths that the reader understands are universal to all people. There is no question that one who reads literature gains worldly knowledge. How often has one read once of the classic and found him/herself understanding the reasons why some facets of life are as they are.
Choosing some moral truths that you have learned from novels, you can use these as supporting details for your thesis that one's knowledge of the world increases by reading literature. Thus, through literature one becomes a citizen of the world.
Interestingly, there are studies that show that business leaders are turning to literature for instruction in character and in analysis of situations. To read about this, see the site listed below.
This can be approached in a variety of ways. One way would be to examine how literature has changed your life. A thesis statement along these lines could be, "Specific works of literature have impacted the way in which I view reality." If a particular work of literature has caused a certain change in how life's meaning has presented itself to you, then the thesis statement could be that a work of literature has literally caused you to reexamine and reevaluate your belief on existence. This would have to be brought out with a discussion of before and after the work was read. I think that the major challenge in such a topic is preventing it from being cliched and excessively maudlin. The way that this can be averted is through being as specific and direct as possible about how this "enlightenment" through literature has happened. Such a tactic would involve specificity and detail to support the idea that literature as "enlightened" you as both reader and thinker.
¿What kind of thesis statment do you need? (argumentative, analytical, etc) ¿and you ask this with reference to what kind of literature? ¿non-fiction, prose, poetry, narratives? can you be more specific s'il vous plaît?