Obsessive love
Heathcliff and Catherine's bond is the engine of the novel, but it is not romantic in any comfortable sense. It is consuming, destructive, and mutual. Their love does not save either of them. It ruins everyone around them and eventually kills them both.
Class and social ambition
Heathcliff's outsider status drives the plot. Catherine chooses Edgar because of class. Hindley degrades Heathcliff because of class. Heathcliff's revenge is partly about seizing the property and status that were used to define his inferiority.
Revenge and its cost
Heathcliff's plan works. He takes Wuthering Heights, humiliates the Lintons, and controls the next generation. But the victory leaves him empty. The novel shows revenge as something that keeps a person alive in the short term and destroys them in the long run.
Cycles of cruelty
Hindley brutalizes Heathcliff. Heathcliff brutalizes Hareton the same way. The pattern repeats until Cathy and Hareton break it. The novel treats inherited cruelty as something that can be passed down like property.
Nature versus civilization
The moors represent freedom, wildness, and emotional truth. The houses represent social order, constraint, and performance. Characters who belong to the moors, like Heathcliff and Catherine, cannot survive inside civilization's rules without breaking.