Soon, the chorus sings, there will be cause for rejoicing. "But you," they say, meaning Orestes, "when your turn in the action comes, be strong." When Clytamnestra cries out "Son!", he must reply, "Father!" Doing this, he may commit the awful deed in innocence.
The chorus opens this section with an ambiguous phrase, asking either how long they will have to wait before they can sing in honor of Orestes, or how long they will have to wait before they can use their speech to aid him in his quest. If the latter is the case, then their wish is immediately granted, as they tell the nurse to tell Aigisthos to come without his bodyguards. This would be consistent with the trend in the Libation Bearers of immediate wish fulfillment. However, even if the latter is the case, the former will also come about, as by instructing that Aigisthos come alone, the chorus ensures that Orestes will be victorious.
Cilissa's role in the play, while brief, is crucial to the plot. On the most obvious level, she brings an altered message to Aigisthos, omitting Clytamnestra's command that he bring his guards. In telling her to do this, the chorus continues its invasive role in the tragedy, operating as actors as well as commentators.
Just as significant, however, is the information that Cilissa gives us about Orestes's upbringing. She says that she cared for Orestes from birth, meaning that she was much more of a mother to him than Clytamnestra ever was. While this custom has been common practice in royal houses throughout history, Aeschylus emphasizes it here in order to discredit Clytamnestra's role as a nurturing mother. As she did not care for Orestes herself, she has far less of a claim on his affections. Orestes feels little to no filial bond with his mother. He is his father's son only.
Cilissa also tells us that Clytamnestra was feigning sadness upon hearing of Orestes's death. While this statement is only an opinion and not necessarily the truth, it does affect our perceptions of Clytamnestra. We are told yet again that we cannot trust her words or gestures. The chorus and the nurse together do everything in their power to discredit Clytamnestra in our eyes, so that we see her not as a mother but only as a cold hearted and manipulative murderer.
After Cilissa's departure, the chorus's prayer serves as a reminder to the audience of all the deities who have played a role in bringing Orestes back home in order to avenge his father. Hermes was his guide, Zeus reminded him of the duties of Justice, and Apollo threatened him with horrible diseases and exile if he did not comply.