Wuthering Heights is a love story. In it, Catherine Earnshaw and Heathcliff grow up together in a dysfunctional household marked by physical abuse and alcoholism. They often escape together to their beloved moors, like two wild creatures. Because they have no one else to lean on, they grow extremely close. By the time they are teenagers, they are deeply in love.
What attracts people to the novel is the strength of their love. As Catherine describes it, it is not the superficial romantic love that most people experience. Few, if any, works of literature describe a passion as wild and intense as this one. It has deep roots, and the two are so alike, so joined, that Catherine can say "I AM Heathcliff." She tells Nellie:
My great miseries in this world have been Heathcliff’s miseries, and I watched and felt each from the beginning: my great thought in living is himself. If all else perished, and HE remained, I should still continue to be; and if all else remained, and he were annihilated, the universe would turn to a mighty stranger ... My love for Heathcliff resembles the eternal rocks beneath: a source of little visible delight, but necessary.
The novel suggests that the two have a bond that transcends death. The intensity of their love and the fact it was thwarted through Hindley's degradation of Heathcliff has shattering effects on both the Earnshaw and Linton families. Catherine marries the wealthy Linton instead of Heathcliff, who responds after her death by wreaking revenge on both families.