How does Charles Dickens choose to tell his tale ?

The comedy involved is pretty dark and ironic. Some of Scrooge's remarks are humorous only because we know Scrooge is miserly and selfish. The Ghost of Christmas Past ironically answers that he is there for Scrooge's "welfare". Consider the exchange in stave one between the charity workers and scrooge:

Are there no prisons?” ‘Plenty of prisons,’ said the gentleman, laying down the pen again.’And the Union workhouses.’ demanded Scrooge. ‘Are they still in operation?’ ‘Both very busy, sir.’ ‘Oh. I was afraid, from what you said at first, that something had occurred to stop them in their useful course,’ said Scrooge. ‘I’m very glad to hear it.’

Scrooge is using rhetorical questioning to get at his dark joke that prisons and workhouses are charity enough for the poor. .