What is the purpose of the sentence following the thesis statement?

The purpose of a thesis statement is to provide a clear, specific argument that will serve as a guide to the reader so she knows what to expect from your essay. A thesis should be related to the question or prompt that your are responding to, but it should provide a specific argument that goes beyond a simple restatement of the subject. The thesis serves as the backbone of your essay, and you will support the claims that you make in your thesis throughout the piece. A good thesis will also help you as the writer know how to structure your essay and when to leave out information that is not relevant to the thesis.