The thematic topic is the subject matter of your story, such as "death," or "man's inhumanity to man." No matter what topic you will be exploring, it will contain large issues, small issues, and everything in between.
In Act One, you need to introduce and establish your theme so that your readers or audience gets a sense of the kinds of issues you'll be exploring. To do this, you have three different approaches available.
1. You could outline the scope of your subject matter with one or more large, definitive dramatic moments. Then, in acts two and three, you would gradually fill in smaller and smaller details, adding nuance and shading to the overall topic as the story progresses. This system is best when trying to apply topics that are often seen objectively or impersonally to everyday life.
2. Conversely, you could begin with the details in Act One, then move to larger concerns as the story progresses. This is a good way to elevate topics dealing with commonplace, mundane, or work-a-day issues to philosophical or global importance.
3. Finally, you could mix it up, presenting a blend of issues ranging from the large to the small in every act. This creates a feeling that the topic is an area to explore, rather than a statement to be understood.
Whichever approach you take, the pattern needs to be set up in Act One so your reader or audience can follow. So determine which approach you wish to take and then create specific examples that illustrate your topic, both in a large and small way.
Finally, pepper these examples into each act as the scope of your topic broadens, narrows, or contrasts the two extremes as it goes.