* Personification: Dickinson personifies Death as a carriage driver, giving him a more human-like presence. By capitalizing "Eternity," she elevates it to a similar level of importance and personifies it as a destination or a being. This reinforces the idea that Death is a guide leading the speaker towards a specific place or experience.
* Emphasis: Capitalizing "Eternity" draws attention to the concept and makes it more significant. It emphasizes the vastness and unknowable nature of the afterlife.
* Poetic license: Dickinson was known for her unconventional use of capitalization. While not always strictly adhering to grammatical rules, her capitalization choices often served to highlight certain words and create a specific effect. In this case, capitalizing "Eternity" adds to the poem's ethereal and mysterious tone.
It's important to remember that Dickinson didn't adhere to traditional poetic conventions. Her use of capitalization often served a personal artistic purpose, adding depth and meaning to her poems.