I find it difficult to understand sentence 2. Can you help me simplify it?

It refers to the first Chapter of Jane Austen's Pride and Prejudice.
Thank you.

1) Chapter one opens with what seems to be an aphorism: it is a universal truth that “a single man in possession of a good fortune must be in want of a wife.”
2) This opening offers an ironic statement about the themes of the novel. The topic of money and marriage are introduced in relation to truth.
3)The author means that everybody agrees on the fact that a rich man must be in need of a wife, and goes on to create a world in which the opposite is shown to be the case, as the mothers of the area prepare to unleash their daughters in pursuit of the two eligible visitors to the neighbourhood.
4) Mrs. Bennet would like her husband to make the acquaintance of Mr. Bingley so as to introduce their daughters to him.
5) Her real worry is to marry off her five daughters. Mr. Bennet, however, does not seem interested and makes ironical remarks. Mr. Bennet’s favourite is Lizzy (line 52) because he thinks she is lively and clever (lines 57-8).

Make sure you use "ironic" not "ironical."

#3 explains the irony -- the assumption about a rich man's needing a wife seems to be questioned.

http://www.sparknotes.com/lit/pride/quotes.html#explanation1
Read the very first paragraph here.

In sentence 2, the author is saying that the opening sentence of the first chapter of Jane Austen's Pride and Prejudice is ironic. The sentence is "a single man in possession of a good fortune must be in want of a wife." This sentence introduces the themes of money and marriage, but it also plays with the idea of truth. It suggests that it is a universally accepted truth that a rich man must be in need of a wife. However, the author goes on to create a world in which this statement is contradicted, as the mothers in the story are eager to marry off their daughters to the two eligible visitors in their neighborhood. So, in simpler terms, the sentence is ironic because it presents a commonly held belief while also challenging it in the story.