| Quote #1
This passage reminds us that it's not just her gender that Viola hides when she cross-dresses as "Cesario." She also disguises her "estate" (meaning her "general condition" and also her "social rank"). Viola's assumed identity as "Cesario," then, suggests that both gender and class are not stable identities. Rather, they can be performed, disguised, and impersonated by just about anyone.
| Quote #2
Even though Sir Andrew Aguecheek is a wealthy nobleman, Maria predicts that his foolish ways and excessive spending will drain his wealth within a year. This, perhaps, is why it's so important for him to marry the wealthy heiress, Olivia.
| Quote #3
Sir Toby is preoccupied with marrying his frenemy, Sir Andrew Aguecheek, to his kinsman, Olivia. To encourage his pal, Toby insists that Olivia will not "match" (marry) above her "degree," which means her social rank ("estate"), her age ("years"), and her general intelligence ("wit"). In other words, Toby says Olivia won't marry the Duke, who is higher ranking, older, and smarter than Olivia. (We know better – Olivia's just not into him.)
History Snack: These comments echo a common Elizabethan idea that nuptials among "equals" made for happier marriages. In 1568 Edward Tilney, one of Queen Elizabeth's courtiers, wrote a famous book called The Flower of Friendship. Check out this excerpt from Tilney's book on marriage – it sounds a lot like what Sir Toby says about Olivia: "equality is principally to be considered in […] matrimonial amity [friendship], as well as years, as are the gifts of nature, and fortune. For equalness herein, makes friendliness."
Of course, even though Toby Belch argues for Olivia to marry a social "equal," he's clearly not at all concerned with his niece's happiness. Toby wants Aguecheek to marry Olivia for selfish reasons. Our theory? If Aguecheek marries Olivia, he'll control Olivia's wealth. Since Aguecheek pretty much does whatever Toby says, Toby would be able to access and to some degree, control Olivia's fortune through Aguecheek. Olivia's situation as an unmarried heiress with a dead father places her in a situation that's similar to that of Portia in The Merchant of Venice. Portia and Olivia are both powerful women with a lot of money and no husband to tell them what to do – until Shakespeare marries them off, that is.