I think that one of the most dominant themes in the poem is the description of how difficult and challenging it is for an individual to ose their hold on what defines reality. The speaker in the poem articulates a condition where there is a finalizing process that depicts the true terror in losing one's hold on reality or the sanity that helps to construct reality. There is a thematic exploration of what happens when one loses their footing or their hold on reality and the process that ensues is not one where there is comfort, but rather a sense of intellectual and emotional atrophy that Dickinson likens towards the rites of death. In this, the poem delves into what it must be like to lose one's grasp on perceived certainty and how all that was once believed is akin to a broken "plank" of reason where there is only uncertainty and fear around the individual. This theme speaks to Dickinson's exploration of elements that others lack vision in seeing. At the time of writing, little thought was given to mental illness or the condition of individuals who struggle with a grasp of reality. Rather than condemning them or dismissing them in a reductive manner, Dickinson explores the thematic terror these individuals must feel as all that was once understood is absent and rapidly eroding.