Edgar sensed his death approaching and worried about Cathy. He had been writing to Linton and now hoped he could console her after his death, believing it was also time for Cathy to return to Wuthering Heights, where her ancestors originated from. Linton had omitted about his illness in his letter Edgar didnt know he was dying as well.
Heathcliff, too, was frustrated. He worried Linton would die before he could marry Cathy, thus preventing him from inheriting Edgars wealth as he had hoped.