Robert Martin is climbing the social ladder – but not in the creepy way that Mrs. Elton is. Although he’s a farmer, Robert manages to earn Mr. Knightley’s respect and confidence. More importantly, however, he’s also an educated man. He’s up on the latest agricultural breakthroughs. You could think of him as a techie: in Austen’s time, innovative agriculture was about as hot as computer programming. We know, it sounds weird, but it’s true. Robert also reads novels, which shows that he’s a man of culture, as well. He also writes a pretty great love letter.
In fact, your econ teacher might call Mr. Martin "upwardly mobile." He’s not quite a gentleman (at least, Emma doesn’t seem to think that he is), but by the end of the novel he’s well-respected.
We’re not saying that he’s always got good judgment, mind you. After all, he falls head over heels for Harriet. (Try saying that one five times fast.) Austen (and Mr. Knightley) wants us to accept their marriage as a "suitable" match: like Mr. Martin, Harriet isn’t quite part of the gentry, but she’s still respectable. Unlike Harriet, however, Robert Martin knows what he wants right at the beginning of the novel. He just has to wait around until Harriet realizes that she actually wants him.