What is one central idea in Stave II of A Christmas Carol?

One could argue that a central idea is regret.

In each of the memories that the Ghost of Christmas Past takes Scrooge to visit, Scrooge seems to have some sense of regret about something or someone.

When he looks back on the boarding school memory, he appears to miss his sister, Fan, but when the Ghost mentions that she had a son, Scrooge is very brief and simply says, "Yes." He is uncomfortable, as if...

One could argue that a central idea is regret.

In each of the memories that the Ghost of Christmas Past takes Scrooge to visit, Scrooge seems to have some sense of regret about something or someone.

When he looks back on the boarding school memory, he appears to miss his sister, Fan, but when the Ghost mentions that she had a son, Scrooge is very brief and simply says, "Yes." He is uncomfortable, as if he regrets not also being close to her only child now that she has passed.

When looking back on the time at Fezziwig's, he is overjoyed at watching the Christmas party and when the Ghost suggests that Fezziwig should not have spent the money making people feel so good, Scrooge defends his former boss. He argues,

“It isn't that, Spirit. He has the power to render us happy or unhappy; to make our service light or burdensome; a pleasure or a toil. Say that his power lies in words and looks; in things so slight and insignificant that it is impossible to add and count ’em up: what then? The happiness he gives is quite as great as if it cost a fortune" (Stave II)

It is then, that he realizes his own power as a boss, and says,

"I should like to be able to say a word or two to my clerk just now! That's all" (Stave II).

Here, he clearly regrets the way in which he has treated Bob Cratchit.

Finally, in the memory with his ex-fiancee, he at first seems very defensive by saying,

"I told you these were shadows of the things that have been,” said the Ghost. “That they are what they are, do not blame me" (Stave II)!

But then immediately asks the Ghost to stop "torturing him," which indicates that he regrets his past actions. If he did not, why would remembering any of this be torture? If he did not, in some way, blame himself for something, he would not be bothered by these memories.