What is the role or function of the Chorus in Sophocles' Oedipus Rex?

The chorus in
Oedipus Rex represents the Theban
elders. The chorus's interest lies purely in protecting the city; and
with this interest in mind, the chorus shows great respect and admiration for their
king, Oedipus, and also great reverence for the gods. Also, with the interests of the
city in mind, they serve the role of portraying a far
greater understanding of humanity than Oedipus
does.

In each ode, the chorus shows either great reverence for the
gods or great respect for Oedipus. The chorus is well aware that the citizens of Thebes
need the gods' protection in order to be healed from their current plague. The chorus
portrays its belief in the gods' power and calls on the gods to use their power to heal
the city, as we see in the chorus's lines:

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I call: my threefold protection from death
[Zeus, Athena, Artemis], shine forth on me. If ever when madness was set upon the city,
you sent away our burning scourge.
(175-177)  

Not only does the
chorus call upon the gods for the city's protection, the chorus is also far quicker to
recognize irrational behavior than Oedipus is, which also stems from the chorus's drive
to heal and protect the city. In its ability to recognize irrational behavior, the
chorus is better able to perceive the weaknesses of human nature than Oedipus is. One
example is seen when Oedipus reacts to Tiresias's horrible prophecy. Oedipus becomes
furious and even accuses both Creon and Tiresias of a treasonous plot. The chorus is
very quick to recognize that Oedipus is behaving irrationally and that the most
important thing is learning how to heal the city, as we see in the chorus's lines, "To
us it seems that both this man's words are your own, Oedipus, were said in anger"
(424-425). 

However, despite the fact that the chorus
recognizes Oedipus's human failings, they remain respectful to their king and find it
very difficult to believe that Oedipus is guilty. Instead, very rationally they argue
that there is no guarantee that the seer is truly wiser than the chorus is and until
they see proof, they will not allow Oedipus's good name to be slandered. The chorus's
rational mind serves to represent a greater understanding of humanity than Oedipus has
himself.