There is a Power whose care Teaches thy way along that pathless coast,-- The desert and illimitable air,-- Lone wandering, but not lost.
Well, well, well, it sure does seem as though our suspicions about the waterfowl being a symbol were correct.
At the beginning of the third stanza, which is almost the half-way point of the poem, the speaker starts out talking about a "Power."
It turns out that this Power is closely involved with the waterfowl. Its (the Power's) "care / Teaches thy way along that pathless coast."
Okay, we need to pause here, because, well, it's kind of weird. These are definitely not your normal uses of "care" and "teaches."
"Cares" does mean care, as in "I want you to take care of puppy," but it means something closer to "guidance" or "direction."
"Teaches" here means much the same thing so that we could paraphrase the lines like this: "whose care directs you along your path."
Speaking of path, here it's called a "pathless coast." The word "coast" recalls the bodies of water we've already seen earlier in the poem.
The thing is, however, the speaker isn't talking about a real body of water here, but the metaphorical sea that is the sky above.
The sky is described as a "pathless coast" because, if you look up at the sky (go ahead, we'll wait here while you do), there doesn't seem to be any boundaries or roads or paths or trails or anything whatsoever.
It just seems like a whole bunch of boundless… air—a "desert," in fact, of "illimitable air" (infinite air, air without limits, in other words: air as far as the eye can see).
So what's a bird to do without any signs or directions up above? Don't fret, fowl-lovers—even though it seems as though there are no paths or anything of the sort up in the heavens above, and even though the waterfowl appears to just be "floating" along, wandering alone, this just is not the case.
The mysterious power that makes its appearance here is actually guiding the whole kaboodle. This "Power" teaches the waterfowl, you could say, the proper path to navigate.
Okay, so things are getting straight up mystical in this part of the poem. What's the speaker driving at? What is this power anyway?
Well, the best answer we have for that burning question is—wait for it—God.
The waterfowl appears to wander, but is in fact not lost or wandering at all. The sky seems pathless and illimitable, but it isn't. It's as if there is some path that the waterfowl is moving along, but we just can't see it.
What's more, our bird buddy follows that path because the mysterious Power (God) guides it along and makes sure it sticks to it.
To sum everything up: the speaker sees a waterfowl floating along in the sky. It appears to wander but it's not wandering. It's movement, its motion, its path—these are all determined and guided by God.
Did you hear that? It's the symbol alarm. The waterfowl has just become a symbol for the ways in which the spiritual power of God controls and directs the physical world.