"Good People" by David Foster Wallace is the story of a young couple trying to cope with an unplanned pregnancy, and it presents the themes of moral choice, fear, courage, religious faith, and a difficult decision. Let's explore some ways you might create a thesis statement about the themes in this story.
First, you might determine which of the story's themes is the primary one and present your case for it. You could say, for instance, that the story revolves around the primary theme of moral choice and argue whether or not the author successfully presents this theme in a way that pushes readers to examine their own moral choices. Choose the theme that you think is most important.
You may also decide to focus on how the author communicates the story's themes. Most of this story is told from Lane's perspective. In fact, what we have here is actually a stream-of-consciousness narrative in which we get Lane's thoughts as he is thinking them. That is why the story jumps around a bit—because people's thoughts do exactly that. Ask yourself if this technique appropriately communicates the story's themes or if it makes them more confusing to understand. Your thesis might be that the stream-of-consciousness technique is highly effective in presenting the complexity of the themes in the story. Or if you choose, you might say something to the effect that the stream-of-consciousness technique is confusing and leaves readers with a shaky understanding of the story's meaning.
Finally, you could argue whether or not you think the story's theme of moral choice is resolved. Consider if there is a choice actually made in the story and, if so, what it is.