What the reader wants to know is not what you plan to say but where you stand. They need some assurance that your point of view promises fresh illumination. They listen to your tone of voice, which conveys your intentions more quickly and clearly than a summary outline of the forthcoming composition. A vigorous introduction, therefore, will seek to establish not so much the subject matter to be addressed as the author’s way of addressing it. It will announce or at least prefigure the argument the author plans to pursue.
Lasch, Christopher. Plain Style: A Guide to Written English. Edited by Stewart Weaver. Philadelphia: University of Pennsylvania Press, 2002.