The tone of this novella really, really shifts from scene to scene, and it is never subtle. As tones go, this one's a bull in a china shop. Mostly, the tone we get depends on whose story we are hearing.
If it's to do with Scrooge, there's usually a vicious tongue-lashing somewhere in the mix. For example, check out the scene when the charity collectors come to ask Scrooge to chip in some money and he wonders how come the poor don't just go to jail or the workhouse or something and leave him alone:
"Many can't go there; and many would rather die."
"If they would rather die," said Scrooge, "they had better do it, and decrease the surplus population. Besides—excuse me—I don't know that."
"But you might know it," observed the gentleman.
"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!"
Seeing clearly that it would be useless to pursue their point, the gentlemen withdrew. Scrooge resumed his labours with an improved opinion of himself, and in a more facetious temper than was usual with him. (1.62-66)
Whew! Now there's a whirlwind of tone shifts if we ever saw one.
The men talking to Scrooge are completely calm and reasonable, pointing out without too much drama that the poor don't want to be in horrible conditions just like everyone else, and that it's a little weird that Scrooge has no sympathy for them at all. Their tone is characterized as being an "observation."
Meanwhile, Scrooge is bitter and nasty and thoroughly snappish, yelling all his answers and generally being a jerk. Not to get all fancy on you, but we have to point out that he switches out the milder subjunctive mood verbs "would" and "might" for the dismissive and brusque indicative: if the poor "would rather" die, well, they must "do it"; he "might" know about them, but chooses to think that "it's not" for him, and that he is otherwise "occupied." Well, fine, Scroogey. Be that way.
Finally, when the dialogue ends and the narrator steps in, the tone is immediately mocking Scrooge, who finishes being a total Grinch and yet somehow obliviously develops an "improved opinion of himself" when any reasonable person would be cringing at such a display of selfishness.
If it's to do with any other character, the tone falls into Hallmark card territory, all sugar and spice and everything nice. The best examples of this tend to come in scenes with the Cratchits, the most idealized family ever. Check them out at the end of their Christmas meal:
Oh, a wonderful pudding! Bob Cratchit said, and calmly too, that he regarded it as the greatest success achieved by Mrs. Cratchit since their marriage. […] The compound in the jug being tasted, and considered perfect, apples and oranges were put upon the table, and a shovel-full of chestnuts on the fire. Then all the Cratchit family drew round the hearth, in what Bob Cratchit called a circle […] the chestnuts on the fire sputtered and cracked noisily. Then Bob proposed:
"A Merry Christmas to us all, my dears. God bless us!"
Which all the family re-echoed.
"God bless us every one!" said Tiny Tim, the last of all. (3.63-68)
This has more sticky-sweet treacle in it than the end of every Full House episode ever. Everyone behaves with ultimate perfection. Everyone is completely aware at every moment of the feelings of all the other family members, and of the importance of the holiday, and is constantly on best terms with everyone else. The kids don't fight. Fight, heck, they don't even yell or talk too loudly.
It's a hoary cliché, but a really powerful one at the time. Reformers like Dickens thought that the only way to overcome the idea that the poor were responsible for being poor was to show just how wonderful they were as people to rustle up a little sympathy. Nowadays, the sentimentality reads as fake and really laid on, but back in the day, it was one of only a few ways to reach those who didn't have regular contact with the working poor.