We paused before a House that seemed A Swelling of the Ground –
If we were unsure before, these lines settle everything. The speaker is going to die. Death just led her to her burial spot!
Your first instinct when you read this might be to scream something like, "Run for your life, lady. He's going to kill you!" But let's not forget how at ease the speaker feels with Death and how calmly she's faced the whole experience so far.
The "we paused" marks the second stop in the poem. The first instance was the beginning of the journey when Death stops to pick up the speaker. So we might guess that this second stop could end their journey.
Using the word "House" to indicate the place of burial is a clever move by Dickinson. Instead of "grave" or "tombstone," which might stir up images of finality and death, she uses a word that we consider synonymous with "dwelling" or even "home." Ever heard someone call a gravesite the "final resting place"? This is a subtler way to say that.
"A Swelling of the Ground" eliminates any possibility that we might think this is not a grave. Think of a freshly-dug place where a dog hides his bone; even after he covers it up there is a little rise in the ground.
The Roof was scarcely visible – The Cornice – in the Ground
These lines continue to explain this burial house, but it gets a little tricky.
A cornice is the pointed part of the roof, and here it's in the ground. So if the highest part of house is in the ground, the rest of it must be too. Further grave evidence.
What part of this burial house can the speaker actually see? It's unclear, but she seems to know what it is and she's OK with it. There's no turning and running for it, as you might typically expect.