Mr. Mustang fears dying and what comes next. He has isolated himself in his own rotting home. Death comes in the shape of a friendly deliver man, but when the old man is consumed by his own paranoia he is left vulnerable to death.
I related this to resolve because the man has either been struggling with the fear of death, his body is ready to go, but his mind is not. Death offers an answer, to take the pain and struggling away from Mr. Mustang, hoping to resolve his inner turmoil.