Death is inevitable. They appear different to everyone. To bad people they appear as their worst nightmare and tortures them with their sins before ending their existence. To good people they appear as something familiar, something kind, something to comfort them before their soul. Death knows there is no afterlife so she wishes to comfort those who deserve it while punishing those who should be punished. That is deaths purpose. And it's their duty to forfill it. Good souls go to the after life 