Final answer:
Heathcliff's intention in Chapter 21 is to oversee the union of Linton and Cathy, a key part of his plans for revenge and consolidation of power in 'Wuthering Heights'.
Step-by-step explanation:
In Chapter 21 of Wuthering Heights, Heathcliff states his intention to oversee the union of Linton and Cathy. Heathcliff is determined to ensure this marriage between his weak, ailing son Linton Heathcliff and Catherine Linton (also referred to as Cathy), for estate and revenge motives. This proposed union is a significant plot point in the story as it represents Heathcliff's continuous effort to manipulate the lives of those around him to gain power and enact his revenge on those he believes have wronged him.