Greetings!
A thesis statement is essentially designed to tell the reader what the entire essay is about. It also usually takes a stance, providing the basis for the argument you will make in the essay. For example, if I were going to write an essay about whether Santa Claus actually exists, I would take a position on one side or the other, and my thesis statement would make that clear: "The figure known in various cultures as Santa Claus, Father Christmas and Pere Noel is more than just an enduring myth; a close examination of the available evidence suggests that the perennial Christmas icon may actually be rooted in fact."
I can't really help you write your thesis without knowing what the four-sentence quote from Charles Beard is. If you'd like to post it here, I'll try to give you more specific direction about how to write not only the thesis, but how to stretch it to five pages!
Thanks,
Sarah, EssayForum.com
Sarah, EssayForum.com