There is no Frigate like a Book To take us Lands away (lines 1-2)
These opening lines basically give away the main gist of the poem – reading a book carries our imaginations far away, even if our bodies remain in the same place.
Nor any Coursers like a Page Of prancing Poetry (lines 3-4)
Here, Dickinson inserts a clever play on words: "prancing Poetry" matches up with the image of the written page as a lively horse ready to trot off with you, but it also plays upon the idea that lines of poetry have metrical "feet," or sets of syllables, that can also "prance."
How frugal is the Chariot That bears the Human soul (lines 7-8)
These final lines emphasize the tremendous importance and power of the written word – the book is the "Chariot" that carries away our souls to far-off lands. That's pretty precious cargo.