What is the theme in Theogony and Works and Days by Hesiod?

Vengeance is a theme that recurs in both "Theogony" and "Works and Days." This is seen in the "Theogony" when Earth plots revenge for her sons, Briareos, Cottus and Gyes, who Heaven hates and hides in a secret place. All of her children are afraid to assist in this plot except Cronos who volunteers. When Heaven lies with Earth, Cronos cuts off Heaven's members. The blood drops fall on Earth, and she conceives Erinyes, Giants and Nymphs. The members are cast into the sea and foam appears out of which Aphrodite grows. Heaven has the Titans by himself and calls them this in reproach for a fearful deed they commit and predicts that they will suffer for this deed. This prediction manifests itself when the Titans battle the Olympian gods and are imprisoned at the ends of the earth.