When Gandalf says, "I am a servant of the Secret Fire, wielder of the Flame of Anor," he mentions his role as a Maia who serves Eru. The Secret Fire, also known as the Flame Imperishable ...

is clear enough, Gandalf's comments about "the Secret Fire" and "Flame of Udûn ... indicating that he's calling upon a massive amount of power to keep Durin's Bane at bay. It conveys the energy ...