This story makes use of a lovely device that, thanks to Shakespeare's Hamlet, we know as a "play-within-a-play." Here it's more like a "play-within-a-story," but you get the idea. The mini-play that takes place shows us a condensed version of what's happening in the larger story. And in order to do that, it has to present us with a character that we can compare to a character in the story we're reading. You with us?
In this case, our set of parallel characters is the Baron Römerstadt/ Jaroslav Kubin (in the mini-play) and author Jaromir Hladik (in the main story). In our "Character Analysis" of Baron Römerstadt/ Jaroslav Kubin, we observe that Kubin's first name, "Jaroslav" looks a whole heck of a lot like Jaromir's mother's maiden name, "Jaroslavski." And, you know, it's pretty natural to see some sort of parallel between the author of a play and that play's main character.
So what do we know about the main character of Jaromir's play? Well, most importantly, Baron Römerstadt/ Kubin is crazy-pants. As in off-the-deep-end, lost-his-marbles kind of crazy. So crazy that he thinks he's the Baron, when really he's Kubin. So crazy that the entire play is really just a delusion taking place within Kubin's head while time stands still.
Sound familiar? Yep, this situation parallels Jaromir's pretty nicely. In fact, the whole "let's imagine this play takes place while time stands still" thing neatly foreshadows the "secret miracle" of Jaromir's writing experience. But what does this foil tell us about Jaromir? Is Jaromir crazy, too? Or is "crazy" just a term we apply to someone who experiences time differently than everyone else around him? Whoa, now we're getting deep.