Till Laura dwindling Seem'd knocking at Death's door: Then Lizzie weigh'd no more Better and worse; But put a silver penny in her purse, Kiss'd Laura, cross'd the heath with clumps of furze At twilight, halted by the brook: And for the first time in her life Began to listen and look.
Finally, Laura seems so close to death and Lizzie can't afford to wait any longer.
She's no longer concerned with the right and wrong, or "better and worse," of it – she's going to go buy some fruit to save her sister.
So she grabs some loose change, puts it in her "purse," says goodbye to her sister, and heads out to the brook.
The "heath" is an area with low, dense shrubby growth, and the "clumps of furze" are clusters of a particular kind of shrub.
It's "twilight," which, as we know, is goblin time.
"For the first time," Lizzie doesn't shut her eyes and plug up her ears – she actually looks at the goblins.