Tragedy, described by Aristotle with Sophocles in mind, is a man who fully understands his own fall from grace.
Oedipus is tragic in this sense, but also because his actions and environment differ so greatly from Job's: Oedipus has no loving God, is aware of his part in his downfall, and repents his existence. Job's sufferings for their differences are not tragic, but make Oedipus appear all the more so.
Sophocles' Oedipus becomes aware of his fault in bringing himself to the sin of patricide and incest, and his awareness of this, more than his fault, creates his tragedy. Job, however, in the course of The Book of Job does not believe that any fault of his own brought himself to suffering. The first companion of Job suggests that Job has committed some sin, the second that Job's sons had, and the third resigned to anything that would leave God safely just. Job denies the validity of these arguments, and calls to God. God, however, does not rationalize his actions, and rather through explanation of His omnipotence convinces Job that He could not possibly be unjust. Job bows to God's superior justice, and yet does not see why he had suffered; thus, Job has no responsibility for the pain God inflicted, feels no worthlessness in the face of purity, and still has his just God. Oedipus, in conflict, avoids predictions of his fate and falls into debauchery; yet the gods and the spinners of fate are not responsible for the reactions of Oedipus. Oedipus sees his own fault in action, as well as the absence of god.
Oedipus' self-consciousness causes readers to empathize, for consciousness allows the readers to experience their own misery. The king evokes empathy rather than sympathy because he is unavoidably and typically human: not only because he is self aware, but also because his social station in life does not make him superior to the rest of mankind. Initially, Oedipus informs his people that he will find and punish the man who killed the former king. He, however, still clouds his superiority by ironically referencing himself as the killer in the line "The man who dared that act will fear no curse." Such words makes Oedipus flawed enough to be tragically human, for the reader knows the king's guilt. Comforting the masses in this situation is an empty gesture, for the reader sees the premonition of Oedipus' future tragedy. He appears more human when calling Teiresias a "sightless, witless, senseless, mad old man" for information indicating his blame for not only the death of the past king, but also for the destruction of the current population. Oedipus never acts as his social status describes, for his only help to his population indicates his fault in creating the need of help. Job, however, is pointedly an example of moral perfection, as God tortures him to prove his devotion, and Job therefore distinguishes himself from any reader of the Bible. This difference between Job and Oedipus illustrates Job as an upright example, and Oedipus as an empathetic but inherently faulty character.
Oedipus is a tragic character not only because he is pathetically human, without a caring god, and fully aware of his guilt, but also because he repents these facts. George Steiner explains in The Death of Tragedy that "absolute tragedy exists only where substantive truth is assigned to the Sophoclean statement that 'it is best never to have been born,'" showing Oedipus as tragic because he would sacrifice his existence for the sake of purity. Job never regrets or repents when he is suffering, for he has nothing to repent. Though his wife suggests that he renounce God and kill himself, he does not, and does not regret his life so much as the absence of God's justice. Even upon speaking directly to God, Job concludes that he was wrong about God, but never admits this as a legitimate fault of his own. Job speaks the line, "I repent in dust and ashes"(Job 42:6) in response to his presumption of the nature of God, and yet God never disproves Job's conception. Job's repentance is only a way for God to re-enter his life, rather than a lamentation of his wrong.
-- some essay I wrote when still enthusiastic and vague. and too distracted to complete anything.