Emily Dickinson uses personification and, in giving Death human qualities, she makes death seem pleasant and courteous. Death is so kind that he takes time to stop for her, since she was too involved to take time indulging the idea of dying. Death "kindly stopped for me" and took her on an extended journey in his carriage.
Furthermore, Death was in no rush, "He knew no haste," and so they took a slow journey. The speaker put aside her labor and her leisure - she did this in appreciation of Death's "civility."
On this journey, Death allows the speaker to witness that which she deems most pleasant, such as a school where children are playing during recess. They pass fields filled with growing grain and witness the sunset. With the sun gone, the speaker feels the chill of dying - also because she is wearing light clothes, since, one can infer, she was not entirely ready for this journey.
Death then takes her to her grave, "a House" that would become a permanent resting place for her body. Her soul, however, would live for eternity for she remembers that, as they were traveling, the horses were heading towards Eternity, implying that she has already passed on and is reflecting on what happened to her centuries before, even though it felt "shorter than a day."