One should not be alarmed that the plot is "spoiled" above; the Greek spectators usually knew the plot beforehand. This can explain, for instance, why characters like
Clymenestra are not "built up" or give no indication of their plans before execution.
The lover of Clymenestra, mentioned above, was
Aegisthus. His desire to kill
Agememnon was to avenge the death of his siblings. Aegisthus' father was
Thyestes, brother to
Atreus and son of
Pelops. After Thyestes seduced Atreus' wife, Atreus served his {Thyestes'} children to him at a "reconciliation banquet".
Myself, I interpreted the message as this; that Athens has made the transition from eye-for-an-eye justice to a more "enlightened" system. I believe the court
Athena establishes is supposed to be the first in the city.