The Infernal Machine is a retelling of the Oedipus tale by Jean Cocteau, designed as a play.
The most important quote comes directly at the beginning:
THE VOICE: He shall slay his father. He shall marry his mother.
This is the essence of the entire Oedipal tale, telling the whole story in two short sentences. Of course, it is more complex than that, but the myth is wholly ingrained in public consciousness, and so leading with those lines instantly sets up the play to follow.
THE VOICE: Watch now, spectator. Before you is a fully wound machine. Slowly its spring will unwind the entire span of a human life. It is one of the most perfect machines devised by the infernal gods for the mathematical annihilation of a mortal.
With this statement, the theme of the play becomes clear; while all events stem from Oedipus's own follies, in the nature of a tragedy he is unable to halt his own destruction. "The Infernal Machine" of the title is in fact Fate, the events that lead Oedipus to unwillingly play his part. Being without empathy, Fate moves on without care for a single life, only concerned with the final disposition of the prophecies.
OEDIPUS: The people of Thebes are looking for a man. If I kill the Sphinx, I will be that man. I will marry Queen Jocasta. She is a widow and...
SPHINX: And old enough to be your mother.
OEDIPUS: The important thing is: she's not my mother.
SPHINX: Do you believe that a queen and a whole people will give themselves to the first man to come along?
OEDIPUS: Of course, if he has conquered the Sphinx.
What are you laughing about? I'm not just "the first man to come along." I'm a prince, my father is the King of Corinth.
Oedipus's arrogance shows in his dismissal of the Sphinx's warnings, although he is not yet aware of her true nature. Finally, his fate is described by Anubis:
ANUBIS: Man's time is folded and hidden in eternity. But I, the God of the Dead, see the whole life of Oedipus unfolded, stretched out before my like a picture in one dimension. All the episodes, from his birth to his death, are pinpricks in the fabric of time.
(All Quotes: Cocteau, The Infernal Machine, Google Books)
Showing again the Infernal Machine, which cannot be stopped or changed, Anubis compares human life to pinpricks in folded fabric, which when stretched out are far apart. Here is set out the predestined fate of Oedipus, and although he was warned, he wilfully blinded himself to the truth, a mental blinding that is echoed literally in the last act.