Austen reserves the right to step into anyone’s mind, but she tends to confine her narrator’s perspective to Emma’s (and occasionally Knightley’s) thoughts. We don’t want you to get too comfortable, though – because Austen’s narrator also likes to throw out some zingers (carefully disguised, of course, as universal maxims or "observations"). Keep a close eye on beginnings of chapters – they’re prime spots for some meditative moments. For example, Emma argues that "where little minds belong to rich people in authority, […] they have a knack of swelling out, till they are quite as unmanageable as great ones. It’s true in the case of Mrs. Churchill, but it’s also true about the world at large. It’s even, we dare say, occasionally a pretty good description of Emma herself."
Funnily enough, Austen’s narrator also offers some deep thoughts whenever a truly shallow or stupid character does something – well, shallow or stupid. After all, it’s Mr. Woodhouse who occasions the observation that "Matrimony, as the origin of change, was always disagreeable." How are we supposed to tell these two types of asides apart? We’re not sure. But the confusion that this causes is part of the fun.
Moments of description also open up to give a sense of broader social consensus. Here’s Emma, thinking about Jane Fairfax: "Her height was pretty, just such as almost every body would think tall, and nobody could think very tall; her figure particularly graceful; her size a most becoming medium, between fat and thin, though a slight appearance of ill-health seemed to point out the likeliest evil of the two."
Notice how Emma thinks in terms of what "every body" or "nobody" would think of Jane, not just of what Emma herself thinks? With some clever wordplay, Austen’s narrator manages to convey to us both Emma’s opinion of Jane and Emma’s opinion about what society as a whole considers to be beautiful. In other words, a character’s opinion in Emma is rarely just a private opinion. It’s also a chance for readers to triangulate that character’s opinions with those of Highbury society as a whole. Austen is remarkably insistent on these constant comparisons: in a way, they nudge us, as readers, into occupy places similar to those occupied by real characters. If you’re reading along and suddenly stop to think, "What would Mr. Knightley say about this?", congratulations. You’re exactly where Austen wants you to be.