I always interpreted it as the point where Harry realizes Dumbledore isn't as strong as he used to be, because Harry's always looks to him for direction but Dumbledore couldn't get through the cave without Harry.
I'm not a big fan of Harry Potter, but my favorite aspect of the books was how Dumbledore slowly seems to lose his "power", going from a near god-like perception to not much more than an old man by the end.
Harry wasn't so wise...