This very short poem directs the reader on how to fill a gap—be that gap something that is left unsaid, a lack of faith, or something else. Her first, rather confusing direction is to “Insert the Thing that caused it –,“ which would actually only make the gap wider, for it would multiply the creation of the gap. She says that if you block it up with something else (“Block it up / With Other”), it will only make the gap larger (“and ‘twill yawn the more –“), because attempts to just fill it with whatever one can will not solve the problem in any meaningful way.
She ends the poem by saying “You cannot solder an Abyss / With Air.” This means that the “Gap” is much larger than originally thought—a gap connotes something much smaller and more easily filled than “an Abyss.” This may be because the gap was always this large, or because the attempts to fill it with meaningless answers only spread it further, until it became an “Abyss.” You can, technically, fill an abyss with air, but this is not her argument—you cannot “solder” it, that is, you cannot unite the two sides, make it into a whole.
This poem is devoted to fathoming nullity or immensity as a spiritual quality. The “Gap” can be read to be a lack of faith, or a specific doubt that prevents one from having true faith. In this reading, by recommending that the doubter fill the gap with “the Thing that caused it,” she is saying that you cannot just ignore these doubts, but must deal with them straight on. This intention seems emphasized in the poems brevity, which doesn’t allow room for avoiding or circling an issue, but must get to it directly.
To “Block it up / With Other,” that is, to try and assuage one’s doubts with answers or assurances that don’t really deal with the question at hand, will only expand the problem, and cause more doubts to arise. This leads to what start as small gaps becoming, instead, abysses, which cannot be soldered by the only thing that is really available to assuage doubt—air—because there can be no real proof of God’s existence. Faith itself requires doubt, for otherwise it would just be knowledge.
This poem can also be read to be a kind of prescriptive for writing a poem. The gap can then be read to be the space between some truth left unsaid, and that truth being declared, and what it takes to fill this gap is the poem that tells that truth. Because Dickinson has serious doubts about any objective truths, however, this solution does not really fill the gap, it only blocks it up temporarily.
Instead, it causes it to “yawn the more,” as every explanation of one truth leads to more questions, and more possibilities for other truths—for other poems. Any one poem, thus, cannot fulfill the work of writing poetry, cannot solve the questions that poetry tries to answer. This again calls attention to this poem’s brevity and disparities in line length, for it does not attempt to solder the abyss, instead it leaves gaps. Poems can provide an answer, which then creates more questions, extending the infinite task of poetry.
The structure of this poem reflects its message—its words work to fill an otherwise blank page, yet in doing so, they point by contrast the emptiness that surrounds them. This is especially noticeable because of the great contrast in line lengths, such that the very short lines highlight the gaps that abut them, and all that is not said there. Although Dickinson was very flexible with form for her time, this poem’s form is very unusual for her, and thus likely was significant in her larger ouevre.