The Same Wind to Twist it

"Now, my bonny lad, you are mine! And we'll see if one tree won't grow as crooked as another, with the same wind to twist it!"

Said by Heathcliff to Hareton after Hindley died, this quote shows so much of Heathcliff's insanity. He basically tells Hareton that he will treat him just as Hindley treated him, hoping that it will end in the same result as his late father.

As insane as it is, this quote is just another reminder that Heathcliff's central reason for living is revenge, which is great than his love for Catherine. 

I think overall, one of the main points to get from Wuthering Heights is to see how intense hatred can be; what kind of person it can make you become. He has so much love for Catherine, but his craving for revenge on Hindley outshines it almost entirely. His lust for revenge keeps him from so much, from true happiness and love.

Don't hate all your life. Sometimes it's best to forgive and forget. And if you can't, then find a different solution. Anything is better than letting that hatred and want for revenge ferment inside you. It kills.