"Safe in their Alabaster Chambers" paints a picture of all the world's dead, sound "[a]sleep" under the stony roofs of their tombs. Nothing, this poem observes, can harm or disturb the dead: they're "safe" from everything, waiting peacefully for the "Resurrection," the Christian Judgment Day when they'll wake up again. To the dead, the world of the living is just so much distant, empty ruckus, rattling overhead; soon enough, all the people making such a great big noisy fuss in the living world will join the sleepers, too.
The poem's tone, at the outset, is a curious mixture of eerie and serene. Take a look at the way the speaker phrases the first few lines:
Safe in their Alabaster Chambers -
Untouched by Morning -
and untouched by noon -
The diacope on "untouched" here makes the dead sound securely insulated from the passage of time. But there's something a little creepy about that idea, too. If one is "untouched" by morning or noon, one must be in pitch-black darkness. And the idea of sunlight touching people (or not) reminds readers that the dead lie quite alone in their "Alabaster Chambers." Those "chambers" themselves, made of translucent white stone, feel pretty ghostly and chilly, too.
Even the poem's shape feels shivery. Dickinson usually wrote in rhythmic common meter, or sometimes iambic tetrameter (lines with four da-DUMs in a row). Here, she breaks from that pattern: the lines here don't use any predictable metrical foot, though they mostly prefer emphatic, front-loaded trochees (feet with a DUM-da rhythm). Not only that, they split in unusual places. Read the poem aloud, and it sounds like it's mostly in accentual tetrameter: that is, lines of four beats apiece, like this:
Safe in | their Al- | abas- | ter Chambers -
But look at the page, and that relatively steady pulse is broken up in all sorts of odd ways. Take these lines, for instance:
Untouched by Morning -
and untouched by noon -
By spreading four beats out over two lines, the poem slows its pace right down. That's fitting for a poem about the inevitability of death: death, confident in its ultimate power, doesn't have to rush in order to catch up with everyone in the end.