"It's not my business," Scrooge returned. "It's enough for a man to understand his own business, and not to interfere with other people's. Mine occupies me constantly. Good afternoon, gentlemen!" (1.65)
Here, Scrooge is more like Dickens's later creations, Mr. Podsnad (from Our Mutual Friend) or Mrs. General (from Little Dorrit)—characters who want to enclose and isolate the unpleasant from their sight because it's just too pesky to deal with.
Scrooge knew [Marley] was dead? Of course he did. How could it be otherwise? Scrooge and he were partners for I don't know how many years. Scrooge was his sole executor, his sole administrator, his sole assign, his sole residuary legatee, his sole friend, and sole mourner. (1.4)
It's interesting that he and Marley basically had the same lifestyle. We initially get the sense that with Marley's death, Scrooge lost his last bridge to humanity. Which of course is immediately shown to be untrue when we meet Fred and Bob Cratchit. Why the fake out?
"How it is that I appear before you in a shape that you can see, I may not tell. I have sat invisible beside you many and many a day." It was not an agreeable idea. Scrooge shivered, and wiped the perspiration from his brow. (1.155)
That's pretty creepy. Also, compare this to how Scrooge watches his own clerk from his little office. He's a bit of a ghost himself.
"The school is not quite deserted," said the Ghost. "A solitary child, neglected by his friends, is left there still."
Scrooge said he knew it. And he sobbed. (2.51-52)
How would our understanding of Scrooge be different if we didn't get this backstory of loneliness and abandonment? Would you just be a full-on Scrooge-hater?
And now Scrooge looked on more attentively than ever, when the master of the house, having his daughter leaning fondly on him, sat down with her and her mother at his own fireside; and when he thought that such another creature, quite as graceful and as full of promise, might have called him father, and been a spring-time in the haggard winter of his life, his sight grew very dim indeed.
"Belle," said the husband, turning to his wife with a smile, "I saw an old friend of yours this afternoon. […]
"Mr. Scrooge it was. I passed his office window; and as it was not shut up, and he had a candle inside, I could scarcely help seeing him. His partner lies upon the point of death, I hear; and there he sat alone. Quite alone in the world, I do believe." (2.138-39,143)
The triple isolation here is a pretty neat trick—Scrooge is watching them talk about his mental and emotional isolation while actually being physically (magically? supernaturally? paranormally?) isolated from them, and while imagining how different his life could have been had he not walled himself off as much as he had.
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 who watched the light had made a fire, that through the loophole in the thick stone wall shed out a ray of brightness on the awful sea. 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 that was like a Gale in itself. (3.93-94)
The images of people trying their best to escape from being isolated are really quite moving, even if they are rather generic and Hallmark-card-like. Hey, if two old cruddy dudes in a lighthouse can make the best of it, well then so can Scrooge.
"Ha, ha!" laughed the same woman, when old Joe, producing a flannel bag with money in it, told out their several gains upon the ground. "This is the end of it, you see! He frightened every one away from him when he was alive, to profit us when he was dead! Ha, ha, ha!" (4.76)
What's great about this scene is that Scrooge's isolation in life is subverted by the way his house and body are invaded and violated in death. It's like a parody of "letting people in."
He went to church, and walked about the streets, and watched the people hurrying to and fro, and patted children on the head, and questioned beggars, and looked down into the kitchens of houses, and up to the windows, and found that everything could yield him pleasure. He had never dreamed that any walk—that anything—could give him so much happiness. In the afternoon he turned his steps towards his nephew's house. (5.47)
The gradual absorption into life is nicely done in the first sentence. Look at the way the verbs very slowly integrate Scrooge. At first he is still on the outside although finally curious about those around him: he simply "went" and "walked" and "watched". But then he starts to interact by "patting" and "questioning" and "looking into". Even there, he builds the interaction, starting small with the insignificant—children, beggars—and only then moving on to people in houses, and finally to the really important, his nephew.
"Now, I'll tell you what, my friend," said Scrooge, "I am not going to stand this sort of thing any longer. And therefore," he continued, leaping from his stool, and giving Bob such a dig in the waistcoat that he staggered back into the Tank again; "and therefore I am about to raise your salary!"
"A merry Christmas, Bob!" said Scrooge, with an earnestness that could not be mistaken, as he clapped him on the back. "A merrier Christmas, Bob, my good fellow, than I have given you for many a year! I'll raise your salary, and endeavour to assist your struggling family, and we will discuss your affairs this very afternoon, over a Christmas bowl of smoking bishop, Bob! Make up the fires, and buy another coal-scuttle before you dot another i, Bob Cratchit!" (5.67-69)
So, there we go—Scrooge is completely recovered. How do we know? Because he is now willing to actually touch another human being. Check out how odd it sounds to see Scrooge poking Bob in the ribs and "clapping him on the back." That's how alien he used to be.
"Do you know the Poulterer's, in the next street but one, at the corner?" Scrooge inquired.
"I should hope I did," replied the lad.
"An intelligent boy!" said Scrooge. "A remarkable boy! Do you know whether they've sold the prize Turkey that was hanging up there?—Not the little prize Turkey: the big one?"
"What, the one as big as me?" returned the boy.
"What a delightful boy!" said Scrooge. "It's a pleasure to talk to him. Yes, my buck!" (5.19-23)
So, are we thinking that the strange third-person asides here—"a remarkable boy!", "it's a pleasure to talk to him"—are the result of Scrooge having forgotten how to speak to other humans? Like, his isolation has literally rendered him unable to have a normal conversation, so he just keeps exclaiming things to his face?