This is a brief but powerful poem on the theme of trauma and its ripple effects on a person's life. Dickinson describes a "wound," unidentified, which grew sufficiently large that every part of her life became subsumed within it. This wound, she imagines, closes the "lid" of a metaphorical coffin upon a person until Jesus, imagined here as the Carpenter, finally nails down that lid when we die. The first stanza of this poem is focused on the opening of the wound, while the second represents how, as that wound opens, our lives can entrap us.
Dickinson does not specify what has caused this wound, but we can assume that it is something grievous and emotionally damaging given the nature of its effects upon the speaker. The title indicates that part of what has allowed this wound to become so significant is that fact that it has not been "admitted" to—that is, the wound has gone untreated and has been ignored by the sufferer. The implication seems to be that one small incident or injury, left unattended out of fear, can become so enormous that it overwhelms every other facet of a person's life.