At Orsino's palace, Viola, now disguised as the page boy Cesario, chats with Valentine. Valentine tells Cesario that if he continues to please Orsino this well, he will advance quickly in the household: after only three days the Duke already trusts him intimately.
In this conversation, which anticipates Viola's intimacy with Orsino, Viola appears disguised as Cesario in the costume she'll wear for the rest of the play.
Orsino enters and asks to speak with Cesario privately. Orsino then tells Cesario he has Orsino's full confidence, and tells Cesario to go to Olivia's house and do whatever he can to receive an audience on Orsino's behalf. Cesario is skeptical, given the firmness of Olivia's resolve not to see anyone. But Orsino is confident that Cesario will be able to persuade her—particularly because, prepubescent, he still looks like a woman: his lips, his voice all resemble "a woman's part" (1.4.35).
This exchange further establishes the degree of trust between Orsino and Cesario. At the same time, Orsino's comment that because Cesario resembles a woman he is likely to persuade Olivia alludes to the ambiguity of Cesario's gender and the confusion it will cause.
Cesario departs for Olivia's house with four or five attendants. But, privately, Viola remarks to herself that she is in a difficult situation: she must woo on behalf of a man whom she herself would like to marry!
Viola's love for Orsino is even more impossible than Orsino's love for Olivia. Disguised as a male servant, Viola can't even reveal her love. But Viola never displays the showy melancholy that Orsino seems to enjoy. Instead, her language is plain, which makes the pain she feels seem more real.