In the nineteenth century, the newfangled steam engine was a byword for power. Just imagine living in a world without planes, trains, and automobiles, where the fastest thing going was a speedy horse. Suddenly, the steam train shows up – and everything is different. "I like to see it lap the Miles" captures both the beauty and the menace of this new technology by emphasizing just how strong and mighty it is. After all, something powerful enough to devour landscapes and plow through mountains is certainly deserving of careful observation and meditation. What makes this new "creature" especially fascinating is the fact that it's manmade – and this child of industry far surpasses its human parents in strength.
Though Dickinson's poem suggests that the mighty locomotive is a domesticated creature, the ambivalent tone of the final stanza implies that man may not ultimately tame this powerful creation.
The absence of human beings in this landscape suggests that human activity has been rendered unnecessary by the arrival of the steam engine.