Three-Planes-Aligned: A deity must have worshippers, for it is the faith of such subjects which gives them power. As converts are made and more come to believe in a god, the more power that god receives.
Conversely, when no one believes in a deity, it withers and dies, joining the corpses of other gods that float on the Astral Plane. It is thus possible to slay a deity by simply forgetting about them.
"When belief in a God dies, the God dies."
"If God is all-powerful, why does He care whether we worship Him or not? Ak just saying..."
— An island native named Ak, The Simpsons
The spirits who had once been mere humans were now elevated to the status of godhood. They fed on the offerings and prayers of not just a small number of close relatives, but instead upon those of an entire nation of people. The stronger these spirits became, the more they demanded of their families to maintain that level of power. Some may perhaps see this as greed, but I have to disagree. It's a simple technicality that a God is going to need a lot more nourishment than a familiar spirit.
— Aaron Leitch, The Ancient Gods and Neo-Paganism
"A gods power comes directly from belief in it... Religion sounds a lot like politics."
— Atsuro Kihara, Devil Survivor
"Humans have the power to assign an answer to phenomena without an answer. The power of observation has the ability to make certain and whole what is uncertain and without form. The Axiom did not give gods the power of observation... Only humans have that power. Humans have the ability to change the answer they have found into faith, and eventually into truth. This can invigorate the gods, but it can also kill them. This is why the gods goad humans to their side, and make them observe things that are beneficial to them. This is the direct cause behind why gods fight over humans."
— Stephen, Shin Megami Tensei IV: Apocalypse
"Have you thought about what it means to be a god? It means you give up your mortal existence to become a meme: something that lives forever in people's minds, like the tune of a nursery rhyme. It means that everyone gets to re-create you in their own minds. You barely have your own identity any more. Instead, you're a thousand different aspects of what people need you to be. And everyone wants something different from you. Nothing is fixed, nothing is stable."
— Jesus, "deleted scene" from American Gods, included in the 10th Anniversary Edition.
The idea of Gods empowered (and possibly created) by worship naturally has a strong attraction for modern fantasy fans: It takes the prevailing social order of democracy and projects it into the plane of divine metaphysics. Instead of Homeric warrior-aristocrats, Middle Eastern despots or Chinese courtier-bureaucrats, Gods become politicians in the sky, dependent on their base, hustling for support. This premise is appropriate and meaningful for modern fantasy. It just doesn't happen to be the premise of Scion.