Whatever we make of the Christmas ghosts and the adventures Scrooge has with them (Is he hallucinating them because guilt has finally gotten to him? Are they actually there?), it is clear that there is a big difference between the real life that he experiences and watches others experience, and the fantastical and chaotic stuff that goes down when he is ghosting around.
Some of the best moments play on the weird moments between the two states, where fantasy gives way to reality, or vice versa, and we can see the rules of the physical world and the ghost world meld together.
For a good example, check out the Scrooge's first encounter with the other world:
Now, it is a fact, that there was nothing at all particular about the knocker on the door, except that it was very large. It is also a fact, […] that Scrooge had as little of what is called fancy about him as any man in the city of London [however] Scrooge, having his key in the lock of the door, saw in the knocker, without its undergoing any intermediate process of change—not a knocker, but Marley's face.
Marley's face. It was not in impenetrable shadow as the other objects in the yard were, but had a dismal light about it, like a bad lobster in a dark cellar. It was not angry or ferocious, but looked at Scrooge as Marley used to look […]
As Scrooge looked fixedly at this phenomenon, it was a knocker again. (1.81-83)
What's great about this is how much effort the narration puts into shoring up reality and rationality in the face of this totally surreal, out-of-this world thing.
Not only do we get some background info (the door knocker has "nothing particular" about it, and Scrooge has the least amount of "fancy" of anyone), but also even the transformation itself tries to be as rational as possible, what with Marley not doing any of the usual scary ghost shtick and instead looking just "as Marley used to look."
The cherry on top of the rationality sundae comes from Scrooge's reaction. Does he freak out? Scream? Call for help? No, he just "looks fixedly" at the face until it goes away. The fantastic has been beaten back by the mundane.
Okay, so the point of the fix-Scrooge project is basically to convince an old man who has walled himself off from human contact to rejoin people, right? Right. So it definitely stands to reason that we get a bunch of compare and contrast scenes of what life is like for those who are isolated and those who seek out the company of others.
On the isolation side, we get the miserable sight of how Scrooge lives today—serving himself some crappy porridge by a too small fire, alone in a building that has no other tenants. Yikes.
We also get a far sadder glimpse into his childhood Christmases, stuck by himself at boarding school with only his imagination for company (and it's not much of an imagination to begin with).
And finally, of course, there is the macabre lonely Christmas of the future, where Scrooge is completely alone even after death. Bummer.
Meanwhile, on the yay-humans! side, we see the equally awesome parties held by Fred in the present and Fezziwig in the past. We also see the dinner thrown by the Cratchits, all full of love, and not so full of food.
But these comparisons are constant and so pointedly blatant that it feels like the narrator is reading over our shoulder, constantly poking us with his finger, and yelling, "Get it? Get it? Huh, huh, do ya?" Um, yes, calm down, dude, we totally get it. Christmas with people is the bee's knees.
So let's do something a bit more interesting, shall we? It's cool to check out the few scenes where people are balanced between isolation and being in the world. For one thing, they're less finger-pointy because they are so much more anonymous than the scenes of people from Scrooge's life. We never really find out who the people in them are, beyond a very generic description from the Ghost of Christmas Present.
First, we meet the miners:
[Scrooge and the Ghost] stood upon a bleak and desert moor […] "A place where Miners live, who labour in the bowels of the earth" […] Passing through the wall of mud and stone, they found a cheerful company assembled round a glowing fire. An old, old man and woman, with their children and their children's children, and another generation beyond that, all decked out gaily in their holiday attire. The old man, in a voice that seldom rose above the howling of the wind upon the barren waste, was singing them a Christmas song […] (3.88)
Then, there are those lighthouse-keepers:
Built upon a dismal reef of sunken rocks, some league or so from shore, on which the waters chafed and dashed, the wild year through, there stood a solitary lighthouse. […] But even here, two men […] Joining their horny hands over the rough table at which they sat, they wished each other Merry Christmas in their can of grog; and one of them: the elder, too, with his face all damaged and scarred with hard weather, as the figure-head of an old ship might be: struck up a sturdy song. […] (3.93)
And just in case we didn't get the picture, meet these sailors, who seem to be having a grander time than poor Mr. Clooney:
Again the Ghost sped on, above the black and heaving sea—on, on—until, being far away, as he told Scrooge, from any shore, they lighted on a ship. They stood beside the helmsman at the wheel, the look-out in the bow, the officers who had the watch; dark, ghostly figures in their several stations; but every man among them hummed a Christmas tune, or had a Christmas thought, or spoke below his breath to his companion of some bygone Christmas Day. (3.95)
As the ghost pulls Scrooge further and further away from civilization, we see that no matter where they are people crave each other's company. Seriously, he stops just short of traveling to Tristan da Cunha, or even the moon, just to prove that all folks need to have some fun is a partner (or two) in crime.
This of course only makes Scrooge's self-isolation seem more and more crazy and unnatural. What is the common thread linking these brief scenes? That the environment around each place is totally barren—the moor is like a "desert", the lighthouse is "solitary", the ship is "far away from any shore"—but that the people are always experiencing togetherness nonetheless. So why can't Scrooge get his act together and get a partner in crime (or two) when he's surrounded by folks in a crowded city?
Oh, and here's a question: Why do you think there are songs being sung in each of these mini-scenes? What's up with that?