How will a thematic statement help me?

Good question! 

By developing a thematic statement, you’re finding your story’s heart, which is equal to figuring out what you want to say to the reader. Now, here’s the magical thing about story — we’re not going to come straight out and deliver our thematic statement word for word to the reader; instead, we’re going to create interesting characters and develop a plot that supports your thematic statement. It’s through the protagonist’s journey that the reader will come to understand your message — without you ever having to spell it out for them. It’s the very definition of “show, don’t tell”!

So, in short, finding your story’s heart will help you construct a story that means something. Your story’s characters and plot will be designed (or tweaked, perhaps, in the case of revising writers) to help get your message across to the reader. When writers skip this step, they develop their characters and plot first, and then have to figure out their message. Often, it’s like fitting a square peg in a round hole. By defining your message now, you’ll save yourself a lot of rewriting in the long run.

I want to assure you at this point that it’s completely fine if your ideas start out quite generic, or even cliché. In fact, it’s quite probable that will be the case. But the more you brainstorm, and the more you think about the story you want to tell, the more your ideas will evolve into something unique to you. At that point, you’ll have the beginnings of a story only YOU can tell. 😊