In this poem, Death is personified. Instead of talking about death as a thing, or even an event, death becomes a person.
More specifically, Death is a gentleman caller who comes to pick up Dickinson, almost as if to take her on a date. She talks about his kindness and "civility," emphasizing his gentlemanly nature. Death takes her on a carriage ride into eternity.
The impact of this use of personification is to change death into something scary and unknown into something honorable that visits everyone.
