If you think about a large wagon wheel as being your complete essay, then the hub (in the middle of that wagon wheel) holding together all of the spokes would most be the thesis statement.

The thesis statement focuses the entire essay.  What are you trying to say?  What reasons do you have for that stance?  What is the main point of the essay?  All of those answers are found in the thesis statement.  It’s important to make sure that you have a clear thesis statement from the beginning, but you can make adjustments as needed along the way — a working thesis statement is used for the drafts to have a general focus until you’ve situated all of your material in the body section.

And, also, all of the spokes are connected to the hub and point to it.  Same goes for all of the reasons and evidence that you include in the essay; all of the material that you’ve included should be connected to the thesis statement and should point back to it.  This section gives more details and strategies to help with thesis statements in your essay.