"Rules and order" is a fancy way of saying "the law," a concept The Dark Knight just loves to push in all sorts of interesting directions. After all, Batman's a vigilante: breaking the laws he finds inconvenient, all in the name of some perceived greater good. Gordon and Dent do the same thing, though on a much smaller scale. Dent's not above pulling strings to get a nice seat at the restaurant, and both of them implicitly condone Batman's existence. But they all believe in rules and order. In fact, one of the reasons Batman's so keen on Harvey is that it means he can stop breaking the law by acting as a vigilante.
Questions About Rules and Order
Why are rules and order so important? What makes the Joker's attacks on them so unsettling?
How do the characters determine which rules are okay to break and which ones aren't? What does that say about them?
Are rules in and of themselves ethical? What are the benefits of them, even if they aren't? Does that mean that the Joker might actually have a case?
What's so vital about Batman's One Rule? What does it prove if he's willing to break all the other rules?
Chew on This
Rules and order have an inherent morality in them here, since they keep Gotham from falling apart.
Rules and order have no inherent morality. It's how the characters apply them that determines their value.