On the front porch sat a cat with gray stripes. Or, a cat with gray stripes sat on the front porch. The first sentence is an example of inversion—a reversal of normal word order, or syntax, especially in the placement of the verb (in this case, "sat") in front of a subject (in this case, "cat"). Although the second sentence might sound more familiar, the first one is certainly ear-catching.
It also fits nicely into the ballad form we talk about in "Form and Meter." But beyond the sound of it, inversion does this cool thing where it helps to delay the meaning of the sentence. You have to read all the way through it to figure it out. It's almost as if inverting the sentence helps Dickinson "dazzle (us) gradually" with the "truth" of this poem.