This scene shows Viola's braveness. She is not afraid to disguise as a man and serve the duke. Moreover, although she is concerned about her brother, Sebastian, she faces up to reality and acts immediatlely. This shows how Viola is decisive and able to react quickly to changing situations.
I prithee—and I’ll pay thee bounteously—Conceal me what I am, and be my aid for such disguise as haply shall become the form of my intent. I’ll serve this duke. Thou shall present me as an eunuch to him. (1.2.54-58)
This scene shows that Maria is a straightforward person that has a mind of her own, especially by her speech. Even though Maria is a servant, she talks very truthfully telling Sir Toby to stop coming late in the night and overly drinking. Even when Sir Toby argues with her opinion, she does not step back.
This quaffing and drinking will undo you; I heard my lady talk of it yesterday; and of a foolish knight that you brought in one night to be her wooer. (1.3.13-15)
By his fluent speaking, Feste proves that the fool is Olivia, not him at once. Feste is convincing and genius with words. His conversation with Maria and Olivia also shows that he is witty, wise, and entertaining.
[The more fool, madonna, to mourn for your brother's soul being in heaven. Take away the foo, gentlemen. (1.5.62-63)
I know his soul is in heaven, fool. (1.5.61)
According to the fact that Malvolio easily believes Maria's words and the forged letter without any doubt, it is shown that Malvolio is very credulous. Also, his daydreaming shows his conceited and pompous character traits as well as his will to improve his position.
Having been three months married to her, sitting in my state, - ... By my life, this is my lady’s hand! these be her very C’s, her U’s and her T’s; and thus makes she her great P’s. It is, in contempt of question, her hand. (2.5.78-80)
This scene shows Antonio's courageousness and loyalty toward his friend. If Antonio lack braveness, he would not be able to decide to follow Sebastian to the Count Orsino's court although he knew had many enemies there.
The gentleness of all the gods go with thee! I have many enemies in Orsino’s court, Else would I very shortly see thee there. But, come what may, I do adore thee so. That danger shall seem sport, and I will go. (2.1.38-42)
Sir Andrew's speech tells that he is a foolish and slow-witted person. He does not seem to be wealthy in knowledge nor skillful in understanding and thinking.
Good Mistress Accost, I would like to know you desire better acquaintance. (1.3.47-48)