The thesis is not the hook that grabs the reader. It is, however, the single sentence that gives direction to your essay. It not only narrows your focus, it also identifies the main points you will evaluate, explain or justify. Because it introduces the purpose of the paper, the thesis statement is often found in the introduction of an essay.
The introduction of an essay can be the most difficult paragraph to write. Not only do you want it to be engaging, but you want to entice the reader to want more. The first sentence needs to grab the reader's attention. Then you want to lead the reader to your thesis. The thesis statement usually works best when it's the last sentence of the introductory paragraph.
When to Use a Thesis
A thesis statement works best with analytical, expository and argumentative essays. Analytical papers break an issue into parts and evaluate the idea presented. Expository papers explain an issue or idea. Argumentative essays make a claim and justify the claim. All of these essays need a point of view on a subject. The thesis statement helps clarify that view. Narrative essays can benefit from a thesis as well. Placing the thesis in the introduction of the narrative tells the reader what to expect.