A theme, or thesis, statement is a specific topic sentence that is to be written at the very beginning of an essay, thesis, or research. Its purpose is to explain with exactness what is the message that the author (or you, if you are the author) aims to send. If it is a research statement, then the purpose is the same; to explain with clarity what is the rationale behind your work and, in other cases, to extract the idea that drives your research.
The placement at the beginning of the work is significant because it prepares the reader for the information contained in the work. In the case of a research article, or a thesis, it helps those who will review your paper to understand exactly what you plan to analyze, or what is your hypothesis, thesis, or idea about something.
Now, the theme sentence is very exact in its content, for it should include the gist of the work to be analyzed. Therefore, the first step is to graphically organize (use a concept map or a web) your thoughts and ideas and take away any descriptor that does not contribute to the overall message.
Think about the question: what have I "heard" the author "say" after reading this? What message do I get out of this piece of literature? Write it down again, this time using active words to explain this message.
An example of a theme statement for "Where Are You Going, Where Have You Been" could be:
The story "Where are you Going, Where have you Been?" illustrates how a lack of self-identity results in the inability to recognize the identity of others, particularly those whose goal is to victimize us.
This main idea, or theme statement, basically tells the gist of the story in one sentence. Notice how there is no mention of the fact that the main character is an adolescent, or a female, etc. This is because the story presents an event that is quite universal; most people, regardless of age, have a lack of self-identity when they do not take the time to fulfill their inherent talents. Also, anybody can become the victim of someone who is two steps ahead of us in being able to conceal their true intentions. Therefore, the theme statement leaves out the details and focuses on the pure message that the author is sending out to the readers.