Nature is a major Dickinson theme, and in "Route of Evanescence" she wants to get at how nature can completely mesmerize someone, even if only for a few seconds. In this poem the speaker doesn't do anything to the natural world. She doesn't pick a flower or even smell one. Nope, all she does is watch. Her attempt to record what she has just seen mirrors the bird's actions. She gives us a few streaks of color, shows the flowers bouncing back to their original state, and just like that, the poem is over (much like a hummingbird might seem to disappear when it jets off before your very eyes). In that sense it's also about our attempts to describe the natural world, even when it remains totally elusive.
By describing the bird using a man-made device like the wheel, the poem suggests that the hummingbird should be given just as much r-e-s-p-e-c-t.
Deep breath, folks. This poem shows us through nature a valuable lesson about slowing down and finding beauty in simple things.