Awake to Love and Beauty! and sometimes 'Tis well to be bereft of promis'd good, That we may lift the soul, and contemplate With lively joy the joys we cannot share.
Sometimes, he says, it can be beneficial to be deprived of good things that you were expecting. That way, you can become happy by thinking about the happiness that you have missed out on. Come again?
If this part of the poem were submitted to a logic class, Coleridge might not get an "A+," but this is Romanticism! Forget logic.
The speaker was expecting to walk with his friends, but since that couldn't happen, his imagination has more than made up for the disappointment. Not that you'd want to have to rely solely on your imagination all the time; only that it can be a useful exercise every once in a while to prove that you can create your own happiness.
My gentle-hearted Charles! when the last rook Beat its straight path along the dusky air Homewards, I blest it! deeming its black wing (Now a dim speck, now vanishing in light) Had cross'd the mighty Orb's dilated glory, While thou stood'st gazing;
For the second time he addresses his friend Charles as "gentle-hearted." It's starting to sound like a pet name.
He tells Charles that he has blessed a bird called a "rook" that flew overhead on the way home to its nest. Here's a picture. He watches as the rook grows smaller and smaller in the distance. He hopes that the bird might pass into the horizon while Charles is watching.
Let's just say that "the mighty Orb's dilated glory" is the most grandiose expression for "horizon" or "sky" we've ever heard. An "orb" is a round object, and "dilated" means "expanded."
or, when all was still, Flew creaking o'er thy head, and had a charm For thee, my gentle-hearted Charles, to whom No sound is dissonant which tells of Life.
Good thing the speaker has a back-up plan, in case the "mighty Orb" thing doesn't work out. The second option is for the bird to fly directly overhead, dropping a "charm" of good luck or fortune right on Charles's head. We just hope that "charm" isn't, ahem, a mess to clean up.
The bird would make a slight or "creaking" sound that can barely be heard in the silence of the evening.
We also have our third and final sighting of the phrase "my gentle-hearted Charles."
The speaker reaffirms that Charles is a guy who knows how to appreciate "Life."
If you were wondering why Coleridge used the word "creaking," which doesn't sound like a particularly attractive noise, here's your answer. Charles can appreciate sounds that might sound "dissonant" or unharmonious to human ears because he knows that they signal life and Nature.
This final line symbolizes Charles's ability to take painful or unpleasant events and harmonize them with larger patterns of nature.