Marriage is essential for a women in terms of financial Security as well as social success. Austen Has incorporated several marriages in her novel to demonstrate the idea of a good Marriage. ie both partners should be on the same social level like Harriet and Robert Martin or even Emma and Mr Knightley. Both partners should also have a mutual understanding between them. This is what Austen is commenting on. As for quotes well, I haven't got my book with me right now, but there is one where Mr Knightley says how Mr Martin and Harriet are a good match but I can't remember the exact quote
Hope that helps!