Well, I think the story might have a theme of isolation and finding one's place in a chaotic world. The message could be that even the smallest and most vulnerable can have inner strength. Maybe it also highlights the importance of hope during difficult times.
I'd say the theme could be about the power of nature and human's insignificance in it. The message could be to respect and be prepared for the unexpected. It might also be a reminder that we're all like that leaf, tossed around by forces beyond our control but still trying to hold on.