Orestes is a literary tool designed to express Sartre's philosophy of freedom. The stages of Orestes's development in the play mirror the necessary stages one must undergo in finding one's freedom. At first, we find Orestes struggling with the common notion of freedom, the idea that one is free if one has no attachments, no commitments, and is well off. This is certainly a kind of freedom, but it is not the true freedom that Sartre wants to make us aware of. It is a "freedom from" something, in that Orestes is not forced to do anything. He is free from persecution, from having to find a job, from any political duties, and from acting by any religious or moral rules. But Orestes rightly feels that in being free from all these things, he is not really free. He feels that nothing is really his: there is no city, community, or family that he can call his own. Furthermore, he has no reason to do anything. He is free from all responsibility.
As the action of the play develops, Orestes understands a different freedom that might be termed a "freedom to." He learns that freedom is not something material. Having money, an education, and slaves does not provide for the most important sort of freedom. When Orestes asks Jupiter to show him a sign, Jupiter obliges. In seeing this sign, however, Orestes realizes that he does not need to act on it: he is free from the power of the gods and from the control of all moral systems. Orestes understands that he is free to kill the tyrants who rule Argos and that if he does not kill them, then this can only be his own choice. The gods may have ordered him to leave, but he is free to interpret their sign as he chooses: he may decide that it means he should leave, but he can also decide to stay.
Jupiter wants to cause Orestes to take action, to leave Argos, by giving him a sign. But Orestes's realization that he is free means precisely that a sign cannot cause him to do anything. Having seen the sign, he can choose how to respond to it. His freedom is the freedom to act, a positive freedom. In killing Aegistheus and Clytemnestra, Orestes creates new values for himself. For example, he commits himself to the idea that freeing people is more important than abstaining from murder. The result is that Orestes cannot feel guilt: his freedom is both the freedom to act and the freedom to interpret the world. Since he has interpreted the world in such a way that killing the king and queen was right, he views his action as having been right. Orestes's development is a movement from the common sense notion of freedom to a deeper understanding of the concept.