The speaker of this poem is a person who has been away from her "Home" for "Years." She has returned home now and finds it difficult to open the door. This leads us to the poem's overall theme. Dickinson makes the point that going home is not always easy, perhaps because of the fear that home has changed in our absence or that we will not be welcomed as we once were.
In the first two stanzas, the speaker has returned home but "dare[s] not enter" the house out of fear that a stranger might address her and ask her business. She does not want to have to explain that she "left" a "Life" there and has returned to resume it, maybe because she fears that there is no place for her anymore.
She uses a simile, comparing the second during which she lingers to "an Ocean" that breaks against her. This comparison emphasizes how powerful and overwhelming her feelings are. She laughs a "crumbling Laugh," using a metaphor that compares her laugh to something that breaks or falls apart, a sign of her diminishing resolve or confidence, and she "fit[s]" her "trembling" hand to the latch in fear that the door will spring open and "leave [her] in the Floor." This metaphor compares the way she feels, so small and insignificant, to the physical act of shrinking down to the floor.
In the final stanza, she reports that she takes her hand away from the latch "As cautiously as Glass," another simile in which she compares the gentleness of her movements now to how she might treat glass, something very fragile and breakable. Finally, she uses another simile when she describes how she flees, "gasping from the House," like a thief. A thief is an intruder, and so this comparison helps us to understand that the speaker, though she has returned to the place she once called home, recognizes that this is no longer her home.