First person Narrator/ one theme "Wuthering Heights"

"I have just returned."  This is an example of first person narrator used throughout the story.  Lockwood is actually the one who is saying the story.  Nelly is explaining the story of Wuthering Heights to Lockwood.  I think I have noticed some themes throughout the story.  One I think is treating someone badly, can always turn bad for yourself also.  Heathcliff was treated terribly by some people, especially Hindly.  He ran away from Wuthering Heights for a while, but then when he was older he returned.  He had cleaned up and he had money.  Hindly saw this and was much kinder to him.  However, it was too late; all Heathcliff wanted was revenge.  He wanted revenge on Hindly, and he also wanted revenge on Catherine for marrying another man instead of him.  I wonder what will happen next!