I tried to think a lonelier Thing

I tried to think a lonelier Thing
Than any I had seen —
Some Polar Expiation — An Omen in the Bone
Of Death's tremendous nearness —

I probed Retrieveless things
My Duplicate — to borrow —
A Haggard Comfort springs

From the belief that Somewhere —
Within the Clutch of Thought —
There dwells one other Creature
Of Heavenly Love — forgot —

I plucked at our Partition
As One should pry the Walls —
Between Himself — and Horror's Twin —
Within Opposing Cells —

I almost strove to clasp his Hand,
Such Luxury — it grew —
That as Myself — could pity Him —
Perhaps he — pitied me —
                                     F570 (1863)  J532

I've had a phrase in my head for years and always want to credit it to Pope but can never ascertain if he said it or not, or who did: "the bird who presses its breast against a thorn to sing". Maybe I got it as a quote in Colleen McCullough's Thorn Birds or something. I'm reminded of it by this poem where Dickinson subjects herself to an intense thought experiment, seeking to imagine the loneliest "Thing" she can. That Thing turns out to be her "Duplicate" or double.
         The poet makes her purpose clear: this is an expedition of "Expiation", some cleansing through an extreme, "Polar" experience. Dickinson has associated northerly polar regions with God before, notably in "My period had come for Prayer" (F525) where she steps "upon the North" to look for God. In "Through the Straight Pass of Suffering" (F187) she compares the faith of the martyrs to a compass needle which "to the North Degree / Wades – so – through Polar Air!" but in this poem she is going for the bitter, remorseless cold where she can feel Death in her bones. 
         Dickinson doesn't give any clues about why she seeks expiation, but it clearly involves making contact with her Duplicate. She probes "Retrieveless things" to "borrow" him. Perhaps that is the realm of the dead for surely all who pass there become retrieveless. She doesn't want to keep or reanimate this soul, but merely form some fleeting connection. Just the idea that such a creature is possible brings her a "Haggard Comfort". Dickinson's surmise that he exists "Somewhere – / Within the Clutch of Thought" strengthens the word likeness of "Expiation" to "Expediton", for on this trip Thought is its own realm. The other meaning of "clutch" – to grasp – suggests the difficulty of this thought expedition. 

The Count of Monte Cristo as prisoner

         What makes the imagined potential creature her Duplicate is that he too is an outcast, someone "Of Heavenly Love – forgot". Dickinson implies that Heavenly Love has been extended to all others; only she and "one other Creature" are forgotten. Could it be that the expiation involves an actual person, now dead? Some soul mate? To reach him she plucks at the partition between life and death as if she were a prisoner and he, "Horror's Twin", was in a cell on the opposite side. The phrase suggests that the plucking prisoner/poet is the Horror. 
         Dickinson makes a similar ambiguous identification with horror in "That after Horror – that 'twas us"  (F243) where a brush with death is like having a "Face of Steel" look at you with a "metallic grin": "The Cordiality of Death – / Who drills his Welcome in". The terror of this encounter explains perhaps why in the current work the poet "almost strove" to take her Duplicate's hand. She doesn't want a closer brush with death than the "Omen in the Bone". 
This encounter is a truly lonely moment. She clearly senses the Duplicate; he seems to be within reach. Yet having struggled to find him, to borrow him, she stops short of touch.  But the poem does end with a bit more than the hoped-for "Haggard Comfort". She imagines a bond of pity between them, and this is "Luxury". It's a dark place when pity passes for luxury, but it is a place of truth. Not many dive into the depths without the safety net of heavenly love.  Who could pity a Horror? Perhaps only "Horror's Twin".