How we cite our quotes: (Line)
Quote #4
There is a Power whose care
Teaches thy way along that pathless coast,--
The desert and illimitable air,--
Lone wandering, but not lost. (13-16)
Time and time again, the speaker confronts the vastness of the natural world. The sky here is "pathless," a "desert," an "illimitable" space. Try looking up at the sky sometime and mapping it, and you'll get an idea of how the speaker feels here.
Quote #5
All day thy wings have fanned,
At that far height, the cold, thin atmosphere,
Yet stoop not, weary, to the welcome land,
Though the dark night is near. (17-20)
The waterfowl models the kind of endurance that we sense the speaker lacks. He flaps his wings for an entire day, despite how cold the air is, despite the fact that night is near, and despite the fact that there is a very "welcome" place to go (the "land").
Quote #6
Thou'rt gone, the abyss of heaven
Hath swallowed up thy form; yet, on my heart
Deeply hath sunk the lesson thou hast given,
And shall not soon depart. (25-28)
These lines recall other "darker" lines in the poem (such as the description of the "cold, thin atmosphere"). Like those, these too paint a very dark picture of nature: the sky is an "abyss" that can monstrously swallow things. Sure, this is a metaphor, but it's still deeply unsettling.