I have now decided that I will also write a commentary on the three plays as a whole considering that the Oresteia appears to be more like a three act play than three separate plays joined together with a common theme. There are a number of things that I would like to talk about in relation to the Oresteia as a whole. However, there are also a number of things that pertain specifically to this play (or act, however you want to look at it) that I will explore at here.
The first this is that like the Libation Bearers, Aeschylus does not use the traditional unity of time and place. Where in the Libation Bearers the unity of place breaks down, in this play, both the unity of time and place break down (unless one can imagine travelling from Delphi to Athens in one day which, by car is possible, but I highly doubt that Orestes had access to a car three thousand years ago). The play begins in Delphi at the Temple of Apollo, and then jumps over to the Aeropagus in Athens where the rest of the play pans out.
The gods play a much larger role in this play than in the others, and in fact the only human character in the play is Orestes. The rest of the characters with speaking roles are all supernatural entities. Clytaemnestra appears at the beginning as a ghost and commands the chorus of furies to take off after Orestes. The other two major characters are Apollo and Athena. The furies are an ancient Greek demons, and in this play they are in pursuit of Orestes to enact judgement upon him for the crime of matricide. However, Orestes is protected by Apollo so the main conflict arises between the furies, who represent the elder gods, and Apollo and Anthena, who are seen as the younger gods.
The Eumenides is basically a courtroom drama, and though the court is a large rock halfway up the hill upon which the Parthenon is built (having been there and stood on it adds a lot more perspective to the play), known as the Aeropagus, which was in effect the Athenian Supreme Court. In fact the play outlines the setting up of the Aeropagus as the high court, as spoken by Athena (pg 170, 1959 Vellacott Translation, the translation that I am using):
from this day forward this judicial council shall / for Aegeus' race hear every trial of homocide. / Here shall be their perpetual seat, on Ares' Hill.'
It is not the play, but rather the myth behind this granite outcrop in Athens, that held such a special significance to the people of Athens.
I will not dwell too much on the courtcase though, since much of this will be outlined in the commentary on the Orestea, but one thing I wish to point out is the deciding vote of Athena. This is another tradition in that if the twelve jurors came to an impass (and we see how the decisions are made in Athens, namely that pebbles are cast into a vase and guilt and innocence are determined by the number of pebbles in the vase, though unlike our system where guilt is determined beyond reasonable doubt, in Athens it was the balance of probabilities and a tie would always fall in favour of the accused) Athena would be given the deciding vote, and she would also decide in favour of the accused.
It is also noticeable that due to the gravity of the crime that was being judged, matricide, its has been decreed that the verdict will not be decided by humans but rather by the gods, as Athena says (pg 163)
This is too grave a cause for any man to judge; / nor, in a case of murder, is it right that I / should by my judgement let the wrath of Justice loose.
The question is not one of guilt or innocence, because Orestes is guilty, and has also been polluted by the crime of matricide. Rather it was a question of which was the worse act: matricide, or the killing of a husband and father - an act that cries out for revenge.
The contest is not between the state and Orestes, but between the new gods and the old. The elder gods, as represented by the Furies, call for the blood of Clytaemnestra to be avenged; it is not the place of a son to kill his mother. To the Greeks this was wrong. However, the young gods call out for the blood of Agamemnon to be avenged, and it was a deed that was placed upon Orestes by Apollo. Thus the struggle is not a question of justice but rather between the new morality and the old.
Some have suggested that acting on the word of a god is a poor excuse for matricide, however it is clear that those who comment on this do not fully understand the nature of Ancient Greek spirituality. This is 4th century Athens, not 21st Century Los Angeles. The Greeks may not have had an established priesthood, but they did take spirituality very, very seriously. It is why I baulk at a lot of the modern movies portraying the Greeks as turning away from their gods. They were not and never did. It is not a contest, as it is now, between the spiritualists and the secularists, it was a contest between the old ways and the new ways. The gods were the gods, no matter how fickle they were, and they were to be respected. If a god told you to do something, you would do it, for fear of earning their displeasure (in the form of divine retribution). It was one of the reasons why they would travel all the way to Delphi to seek their guidance.