How does Aristotle explore the relation of poetry and reader/audience through his definition of tragedy?

In his Poetics, Aristotle says that
tragedy is the greatest of literary art forms because its agents and devices are better
than us (the reader/audience).  Whereas comedy is more realistic, even below us in its
aims, tragedy leads man to question the moral choices and responsibilities of being a
human and, therefore, enters the religious and ethical
realms.

His definition of tragedy is as
follows:

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Tragedy, then, is an imitation of an action that
is serious, complete, and of a certain magnitude; in language embellished with each kind
of artistic ornament, the several kinds being found in separate parts of the play; in
the form of action, not of narrative; with incidents arousing pity and fear, wherewith
to accomplish its katharsis of such emotions. . . . Every Tragedy,
therefore, must have six parts, which parts determine its quality—namely, Plot,
Characters, Diction, Thought, Spectacle,
Melody.

So, the embellished
language (the poetry) must be elevated, higher in purpose and more beautiful than
everyday speech.  Since early Greek tragedy was religious in nature, its language was a
form of praise.  It is much like a combination of a poetry, sermon, and hymn from a
church service.

The chorus is the ideal reader/audience in
Greek tragedy.  Through their melody (embellished language, poetry, choral odes), the
chorus not only informs the audience how to act or respond to the action of the play,
but they give unity to the plot.  Since they are always on stage, and since the audience
is always watching, they are an intermediary between the actors and
audience.

In the end, the embellished language by the
actors and chorus must move the reader/audience toward a katharsis,
a purgation of pity and fear.  The audience must pity the tragic heroes and fear that
the tragic heroes' fate may be their own.