So along with youth, good looks, and wealth, you have the wisdom of far riper years; your mind is free from prejudice and superstition; you have no family ties, no religion, and no calling; you are free to turn your hand to anything. But you know better than to commit yourself – and there lies your strength. (1.1.96)
According to Sartre, the Tutor is right – in a sense. Orestes is free. And yet, he makes no use of this freedom until he chooses and acts. The Tutor would be wrong then, when he advises Orestes not to commit himself. Orestes isn't free until he acts on that freedom by committing himself to an action of his choice.
Some men are born bespoken; a certain path has been assigned them, and at its end there is something they must do, a deed allotted. So on and on they trudge, wounding their bare feet on the flints. I suppose that strikes you as vulgar – the joy of going somewhere definite. (1.1.97)
Pay close attention to the various speeches in which Orestes discusses the idea of a "path." There is a joy in having a path, he knows, but it is not until later that he discovers the importance of choosing one's own. The Tutor seems to see two options: being path-less, or being committed to a path that someone else has chosen for you. Orestes will later discover that he can commit himself to a path he has chosen for himself. In this way he maintains his freedom while still giving himself the weight and substance he desires.
A king should share in his subjects' memories. […] If there were something I could do, something to give me the freedom of the city; if, even by a crime, I could acquire their memories, their hopes and fears, and fill with these the void within me, yes, even if I had to kill my own mother… (1.1.105)
When Orestes ultimately does kill his mother, is it for self-serving purposes, or selfless ones? Does he do it, as he says here, to fill the void within himself, or does he do it, as he claims in his closing speech, to free the people of Argos?
You will […] murmur to yourself, "It wasn't I, it could not have been I, who did that." Yet, though you disown it time and time again, it will always be there, a dead weight holding you back. (1.1.206)
Sartre explored this problem – the difficulty with reconciling the self of the past with the self of the present with the self of the future - in Being and Nothingness. He believes that man re-created himself in every moment through every choice and action.
I do not know who you are, young man, nor what brings you here, but your presence bodes no good. Electra hates me – that, of course, I always knew. But for fifteen years we have kept the peace; only our eyes betrayed our feelings. And now you have come, you have spoken, and here we are showing our teeth and snapping at each other like two curs in the street. (1.1.210)
Clytemnestra here claims that Orestes is responsible for causing this vehement argument. What is it about Orestes's presence that drives these two to fight?
[Falling on his knees] I stink! Oh, how I stink! I am a mass of rottenness. See how the flies are teeming round me, like carrion crows… That's right, my harpies; sting and gouge and scavenge me; bore through my flesh to my black heart. I have sinned a thousand times, I stink of ordure, and I reek to heaven. (2.1.28)
It's important to note that the citizens of Argos want the flies – their punishment is self-imposed. This man also willingly dehumanizes himself by referring to his flesh as "carrion."
What are you, Electra, but the last survivor of an accursed race? (2.1.68)
The King tries to control Electra through the idea of "destiny." As far as an existentialist is concerned, there is no such thing as destiny. Electra might have messy family history, but she can choose how this history is going to affect her. As Sartre writes, she alone has the power to interpret her facticity (more on that in "Character Analysis").
In Greece there are cities where men live happily. White, contented cities, basking like lizards in the sun. At this very moment, under this same sky, children are playing in the streets of Corinth. (2.1.77)
Notice how the sun is interpreted differently at different moments in the play. It's up to each person to decide the meaning of elements in nature.