The Brain — is wider than the Sky —

The Brain — is wider than the Sky —
For — put them side by side —
The one the other will contain
With ease — and You — beside —

The Brain is deeper than the sea —
For — hold them — Blue to Blue —
The one the other will absorb —
As Sponges — Buckets — do —

The Brain is just the weight of God —
For — Heft them — Pound for Pound —
And they will differ — if they do —
As Syllable from Sound —
                                                                       F598 (1863)  J632


Each stanza of this popular poem provides an interesting metaphor to ponder, each one manifesting the wonders of a three-pound human brain encased in its dark skull. The first two stanzas deftly channel into the final where Dickinson engages cryptically in the ongoing theological question of whether God is created in the brain or the brain is created by God. (By "brain" I am reading "mind" throughout the poem. Dickinson's using "brain" adds interesting contrast: the compact physical thing versus the diffuse and abstract.)
The first stanza goes up and wide, spanning the heavens: the "You", no doubt a generalized reference to the reader, can stare at the sky day and night, experience weather and seasonal changes, and take it all in "with ease" and space to spare. In Dickinson's container metaphor the brain can hold not only the sky but "You" as if it had unlimited storage capacity. 
Next, Dickinson likens the brain to a sponge. It can absorb an entire sea just as a sponge might sop up a bucket of water. The brain here is the limitless blue of sea and sky.

Balance scales; photo by L.Miguel Bugallo Sánchez 

        So far the brain is wide and deep; it can contain and absorb. The third and final stanza makes the startling claim that its weight is "just the weight of God". We don't think of either consciousness or God as having weight and neither did Dickinson. But perhaps that is her point. Can a brain greater than sky or sea affect on its own the unfurling of a rosebud or the safe return of a soldier to his family? Can God? Is it possible that there is some fundamental unity between consciousness/brain/mind and God, or that more particularly the first engenders the other? I can't imagine Dickinson writing that last stanza without those questions in mind.
But if there is any difference – and Dickinson notably includes an element of doubt – it is what distinguishes "Syllable from Sound". While syllables are always sound (or written representations of sound), sound is only occasionally syllables. Perhaps Dickinson is implying that humans give voice to creation and creation's Source.

I love this thought-provoking poem.