The novel is set during the 19th century New Zealand gold rush—which, in case you weren't aware, was actually a real thing. Although Catton may have taken some "liberties" with the actual history of this period, there's no doubt that her choice to set her story within a gold rush, with all the promise and possibilities that come with that kind of thing, is incredibly important to understanding where the characters are coming from.
For example, even when Balfour is trying to sympathize with the sad tale Moody has just told him about his family, he ends up just bursting with enthusiasm about the kind reinvention that you can find in a gold town:
"I'm sorry for you, Mr. Moody, and commend you, both. But yours is the way of the goldfields, is it not? Reinvention! Dare I say—revolution! That a man might make new—might make himself anew—truly, now!" (I.1.148)
It may not be the most sensitive of reactions, but Balfour is just so infected with the hopefulness of the times that he can't help himself from telling Moody just to forget the past (ha, easier said than done, as the book goes on to prove) and embrace a very different (and lucrative) future.
Sure, perhaps the book pays less attention to the nitty gritty of historical details of its era than some other historical fiction, but it definitely uses the historical context to great effect.