The "secret fire" mentioned by Gandalf is a part of J.R.R.'s cosmology which he sets out in the Silmarillion. Essentially it's the divine spark given by the creator (Ilúvatar) which gives life, awareness and free will to sentient beings. Melkor, jealous of the power of the secret fire seeks to control it himself and this precipitates his fall from grace. Melkor and his follower Sauron want to create life in their own image but are able only to twist and distort the light of the secret fire, creating monstrous beings like orcs.
Gandalf's power stems from his awareness of the secret fire, his nature as a guardian of the light and his commitment to service. He is fully aware that light trumps shadow and that awareness is what gives him the power over the Balrog.
[/nerd rant]
Gandalf's power stems from his awareness of the secret fire, his nature as a guardian of the light and his commitment to service. He is fully aware that light trumps shadow and that awareness is what gives him the power over the Balrog.
[/nerd rant]