Final answer:
Oedipus is eager to question the shepherd who witnessed the murder of Laius to bring the killer to justice and end the plague, unaware that it would lead to the revelation of his own actions fulfilling a grim prophecy.
Step-by-step explanation:
Oedipus is eager to question the man who witnessed Laius' murder because he is determined to find the culprit and bring justice, thereby ending the plague afflicting Thebes. The information that a shepherd was with Laius on the day of his murder and now lives in seclusion raises Oedipus's suspicion, especially since he recalls an incident from his own past where at a crossroad, he killed a man during a fight. This stirring connection leads him to believe that by interrogating the shepherd, he might unveil the truth, assuming the shepherd possesses knowledge that could either confirm or deny the involvement of bandits, which would contradict the prophecy that Laius was to be killed by his own son.
However, as the play progresses, it is revealed that Oedipus himself is the unwitting fulfiller of the very prophecy he’s trying to solve, making the shepherd's testimony critical to uncovering his own past and the awful truth that he killed his father and married his mother.