How do the letters relate to Dickinson’s poetry?
There are many examples, but here’s just one: When Dickinson loses her housekeeper, who quit to get married, she writes that she really misses the maid—a common enough statement—but then writes, “To all except anguish, the mind soon adjusts.” This merging of the minor and the vast is a key trait of Dickinson in the poems and in the letters. The leaps of imagination are stunning. One needs privacy and silence, and flourishing genius, to live in such a realm. Otherwise, one stops at, “Gee, I miss Maggie the maid so much.”
The letters are part of the poetry, launching pads for her crises, joys, and observations. Being in seclusion, everything is pitched high, allowing her to roam free and to explore states of awe. There is nothing to hold her in check. The concrete becomes the abstract. The personal becomes the universal. Her letters transcend the factual and biographical and ascend into the realm of poetry.