I'm no English expert but I did study this text for vce last year and here's just my 2c.
Firstly think of your 'contention', that is, what is your stance on the topic. Do you agree, disagree, or a bit of both? This is what you will have to make clear in your intro.
Personally, I'd agree with the topic - it is enthralling (kind of) in that there's a happy ending, and that we see a huge transformation in Scrooge's attitude, but it is written by Dickens as a warning to society about the dangers (in the form of Ignorance and Want) that society faces if we act like Scrooge eg neglecting family, being stingy, and other general all round unpleasantness. I'd discuss how Dickens wanted society to understand its social responsibility (broader obligations to society) eg as a wealthy middle class man Scrooge has an obligation to be charitable to the working classes (Cratchit) and responsibilities as an employer. Marley tells Scrooge that "the common welfare" should have been his business. Through the novel Dickens is trying to tell/educate the respectively well off in society that they had an obligation to look after the less fortunate as they were all human, before things like Ignorance and Want plague society.