[Aiwendil]

Kuruharan:

The quotes you give are surely important; but we also have:

'They say,' answered Andreth: 'they say that the One will himself enter into Arda, and heal Men and all the Marring from the beginning to the end. This they say also, or they feign, is a rumour that has come down through years uncounted, even from the days of our undoing.'

He is already in it, as well as outside,' said Finrod. 'But indeed the "in-dwelling" and the "out-living" are not in the same mode.'

But they speak of Eru Himself entering into Arda, and that is a thing wholly different.

All from the "Athrabeth Finrod Ah Andreth" in HoMe X.

So either:

1. Andreth's story of the "Old Hope" is without basis in fact,
2. Tolkien changed his mind at some point, or
3. The statements in Letters are to be taken to refer only to the time of the action of the stories, and there is to be an incarnation of Eru in a later age.

But in any case this has little to do with the question of the Secret Fire and less to do with Mount Doom.

But I think you are right here:

Quote:
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.


Here we have a statement that can be interpreted metaphysically, where the above statements can only be interpreted physically.

I have always thought that the Secret Fire/Flame Imperishable was the part of Eru that embodies creativity (i.e. not just the ability to think of things but the power to make, to generate something out of nothing). Cf. Ainulindale:

'Of the theme that I have declared to you, I will now that ye make in harmony together a Great Music. And since I have kindled you with the Flame Imperishable, ye shall show forth your powers in adorning this theme, each with his own thoughts and devices, if he will.'

' . . . And I will send forth into the Void the Flame Imperishable, and it shall be at the heart of the World, and the World shall Be'

I do not, then, see the Secret Fire as a great pool of magma beneath the earth's surface; rather, it seems to be the metaphysical power behind Arda's existence.

It also doesn't feel quite right to say that Sauron was harnessing, especially through such mundane means, the Secret Fire - that which Melkor could never find, and which Gandalf names in opposition to the flame of Udun.