This seems to be one of Dickinson's poems that is based on the theme of nature and of the kind of danger and beauty that it represents. Even though the experience in this poem is later said to be a dream, what is interesting is the way in which the speaker's action of tying up the worm to take it out of her room then results in the arrival of a snake that takes the form of the worm who has grown and matured. Note the way that Dickinson relates this "with creeping blood." The power and strength of the snake are indicated through the way that it is said to be "ringed with power."
The conversation that Dickinson and the snake have, where the snake seems to take Dickinson to task for not showing him any cordiality seems to point towards the central theme of the poem. We must not underestimate nature and its power and strength, which can represent a real threat to us, as the way in which the speaker flees the snake demonstrates. Nature is not something that can be domesticated by man, but actually has the power to provoke fear within us.