Why do the Furies pursue Orestes in the Oresteia?

In the Oresteia, the Furies (or Erinyes) pursue Orestes because he committed the crime of matricide by killing his mother, Clytemnestra, to avenge the murder of his father, Agamemnon.12

As the chthonic goddesses of vengeance, the Furies act as the personified incarnations of the curse invoked by Clytemnestra as she lay dying. Although Orestes carried out the act at the command of the god Apollo, he is nonetheless haunted and driven to madness by the Furies, who seek retribution for the blood-tie he violated. The pursuit continues until Orestes stands trial in Athens, where the goddess Athena secures his acquittal, ultimately transforming the cycle of retributive violence into a system governed by the rule of law.3142