This is only beginning to come to me during this reading - my fourth - and it's one of my favourite aspects of JA. The first chapter is quite short, but by the end you know as much about Mr.and Mrs. Bennet (and Lizzy!)as you would have if JA had spent pages detailing them both. Every sentence serves its purpose.
This is true of the rest of the book. Even a small conversation or event - such as Darcy's listening to Lizzy talk to Sir William (Chapter 6)tells us a great deal about the characters. Each time I re-read P&P I get more and more out of it.