Once you have considered your purpose and audience, you can begin to articulate and write down a thesis statement for your text. Even if you decide not to include an explicit thesis statement in your text, it is worthwhile developing a thesis statement as it will help you narrow down your focus, convey your purpose, and organize your text.
A thesis statement is essentially the purpose or goal of the text, beyond just a broad goal such as to inform or to argue. It should not only convey purpose, but also narrow your topic to one main idea and perhaps include a claim.
For example, one could write the purpose of the pre-writing section as follows:
"The purpose is to provide future writers with information about writing in a technical context.”
Now, that is quite vague and perhaps not very useful.
A more precise thesis statement could help us to narrow down our purpose as well as express our purpose more precisely. For example, after revision, our thesis statement might read:
"The purpose is to inform future writers of the crucial pre-writing steps of defining purpose and audience through reader analysis"
We now have a much better idea of our purpose as well as a more clear expression of the central topic. With a well-formed task directive or thesis statement, the writer has come a long way towards a well-written text in terms of knowing the reader and the purpose of the text.
Imagine these two statements appeared in the introduction of a text. The second statement gives the reader much more of an indication of what's coming next: e.g. the focus of the paper, the purpose behind the communication, and clarifies some sub-topics/foci. The first statement would give a general direction, but will leave your readers guessing to some degree, which would be less effective.