The Gods as Imperfect Beings
Though the gods described in Theogony are in fact divine, they are not perfect. A major aspect of Theogony is the imperfection and almost human-like qualities of the gods. None of the gods are all-powerful or all-knowing, with each god having their own skill or specialty. Even Zeus, the king of the gods, is not perfect, and often makes mistakes more akin to humans than gods; though married to Hera, he frequently fathers children from mortals. The gods are imperfect, causing interpersonal problems between them.
Succession
In terms of succession, Theogony demonstrates that although certain gods may reign supreme for the time being, that does not mean that they will remain in power. This is seen with Kronos' dethroning of Uranus at the request and support of Gaia. Succession is seen again when Zeus ascends to the throne after defeating Kronos for devouring his siblings. In fact, succession is such an important theme that the gods themselves are aware of their own impermanence as rulers: Kronos only ate his children because he knew that one of them would usurp him.
Primordial Waters
Primordial waters are a pivotal theme in any creation myth, and Theogony is no different. The poem begins with nothingness, Chaos, in the form of primordial waters. At the beginning of time, before gods and humans inhabited the universe, only this water existed. From this water, the first gods (Gaia, Eros, Hemera, and Nyx) are born, with their own children subsequently born after.