In her work, Dickinson addresses pretty much everything: religion, life, love, family, and especially death. Not to sound overly morbid, but I feel she is at her best with poems that concern death and the afterlife. Here's one of my favorites, taken from Brooklyn College English website:
Because I could not stop for Death,
He kindly stopped for me;
The carriage held but just ourselves
We slowly drove, he knew no haste,
And I had put away
My labor, and my leisure too,
For his civility.
We passed the school, where children strove
At recess, in the ring;
We passed the fields of gazing grain,
We passed the setting sun.
Or rather, he passed us;
The dews grew quivering and chill,
For only gossamer my gown,
My tippet only tulle.
We paused before a house that seemed
A swelling of the ground;
The roof was scarcely visible,
The cornice but a mound.
Since then 'tis centuries, and yet each
Feels shorter than the day
I first surmised the horses' heads
Were toward eternity.
There's some pretty cool imagery in here, including Dickinson's description of Death as "kindly." Typically, we don't associate the Grim Reaper as a nice guy, but Dickinson portrays him here as someone with a bad reputation. To her, Death's job is to curry her from this life to the next.
Do you see where Dickinson's speaker's life flashes before her eyes? "We passed the school, where children strove / At recess, in the ring" represents childhood. The "fields of gazing grain" is the mid part of life, adulthood, and "the setting sun" represents our old age. I always find it extraordinary that even in Dickinson's time, one's life flashing before the eyes before death was a common enough occurrence to mention it in a poem.
Dickinson's speaker only finds panic as they approach the next life, the "swelling of the ground." This represents the unknown afterlife, the one that we on Earth question and wonder about so constantly. It's fascinating to me she separates her fear of death from her fear of the afterlife.
Keep reading! There's tons of analytical sources online that offer different opinions about Dickinson's work besides my theories. I'd love to know what you've come up with!