In Oedipus Rex, how can the choragos refer to God--"How can God's will be accomplished best?"--when I thought the Greeks were polyatheists?

First, the Ancient Greeks weren't necessarily
polyatheists. They are better classified as polytheists with some elements of pantheism.
Keeping that in mind, the origin of Greek theatre plays a significant role in the
traditional elements found in Greek plays. The Greeks originally created theatre to pay
tribute to Dionysus--a Greek god. Thus, Greek playwrights, whether they personally
believed in a Supreme Being(s) or not, would have been obligated to include references
to god(s) in order for their plays to fit the theatre's festival spirit and
traditions.

Similarly, the Ancient Greek playwrights/bards
portray god as a moral/cultural code by which the Greeks were supposed to live rather
than depicting a specific higher power figure. In Sophocles'
Antigone, the chorus and Choragos serve as reminders to Creon of
what he should do; they are a conscience of sorts. Likewise, the
oracle and prophet Tiresias often deliver messages to characters, messagethat contain
omniscient elements or moral guidance from a godlike power. This concept from Greek
drama not only enables the playwright to pass down Greek traditions, but it also
promotes a type of absolute morality, which Aristotle later focused on in his discussion
of ethics.