Secret Fire

In J. R. R. Tolkien's mythology, the Secret Fire and Flame Imperishable are references to the life-giving and reality-bestowing power imparted to the world, Eä, by Ilúvatar.

In an early draft of the "Music of the Ainur", Tolkien writes: "...Only one thing I have added, the fire that giveth Life and Reality, and behold, the secret fire burnt at the heart of the world.". To the extent that "secret fire" remained in later drafts, the initial intent is clear, "secret fire" is the divine "spark" of life. Gandalf's reference to being a servant of the Secret Fire thus implies he is a servant of Ilúvatar. Tolkien described it as similar to the Christian Holy Spirit. Melkor, desiring power equal to Ilúvatar, sought for it in vain. Melkor's desire for the Secret Fire led to his rebellion against Ilúvatar (reminiscent of the fall of Satan in Paradise Lost).

Therefore Ilúvatar gave to their vision Being, and set it amid the Void, and the Secret Fire was sent to burn at the heart of the World; and it was called Eä.

— "Valaquenta", The Silmarillion

The Secret Fire is also part of all Fëar: it is that Gift which makes sentient beings capable of independent will. Thus, while the Vala Aulë created and animated the first Dwarves, and even began to teach them language, they acquired will independent of his only through the intervention of Ilúvatar. Speaking of Orcs, Frodo explains this to Sam:

"The Shadow that bred them can only mock, it cannot make: not real new things of its own."

— The Return of the King VI 1: "The Tower of Cirith Ungol"

Gandalf the Grey refers to the Secret Fire when facing Durin's Bane at the Bridge of Khazad-dûm:

"You cannot pass," he said. … "I am a servant of the Secret Fire, wielder of the flame of Anor. The dark fire will not avail you, flame of Udûn. Go back to the Shadow! You cannot pass."

— The Fellowship of the Ring II 5: "The Bridge of Khazad-dûm"