Please comment on the theme of nature in Oedipus Rex by Sophocles.
This is a very sophisticated question. Nature is related to the word, natural in Sophocles' Oedipus Rex. Let me explain.
In the beginning of the work, there is huge plague in Thebes. This plague is against nature. What there should be is health and a good cycle of harvest and life. This cycle of nature is broken and what the Thebans are experiencing is something unnatural. It is no wonder, this catches the sight of Oedipus, who seeks to solve this problem.
The irony of all of this is that Oedipus is also unnatural in his actions, even if it is unwittingly. He killed his father and married his mother. This causes not only the plague, but also his blindness.
There is another irony, Tiresias is unable to see, something unnatural, but yet he has supernatural sight. When Oedipus finally sees who he is and what he has done, presumably the plague in Thebes lifted and nature is back to normal.