This is not another "Who was Tom Bombadil" question. Close to the end of ROTK Gandalf tells one of the Hobbits that it's time for him to go and have a long talk with Tom Bombadil. Was there anything significant to this talk? Does anyone know what it would be about, etc?
With the understanding that
- Bombadil was clearly depicted as the oldest being in Middle Earth (He tells the Hobbits this in their encounter with him ... "Tom was here before the river and the trees"(FoTR))
- Gandalf was one of the Maiar, which were spirits created before Middle Earth took the shape it was in when the elves first awoke (Olórin he was called before Gandalf, cited in LOTR and The Silmarillion)
it is easily argued that these two were kindred spirits from waaaaay back.
Tolkien humanizes Gandalf in his role as "old man", in that he hungers to have the freedom (after his long labors against Sauron, who was also once one of the Maiar*) to sit down over a pipe and have a long discussion or reminiscence with someone more like him, someone who remembers *the old days1.
There are very few beings on Middle Earth who could fulfill that hunger: Bombadil2 was one such.
I am going to have a long talk with Bombadil: such a talk as I have not had in all my time. He is a moss-gatherer, and I have been a stone doomed to rolling. But my rolling days are ending, and now we shall have much to say to one another." - The Return of the King (Homeward Bound)
1 As @corsiKa pointed out, Gandalf had recently defeated three other Maiar: (Durin's Bane aka the Balrog (corrupted ages ago by Morgoth), Sauron, and Saruman (who had been corrupted by the desire for Power, or as Gandalf put it in LOTR, wanting to "become a Power")). These three were, back during the Great Music described in The Silmarillion, originally spirits of the same kind. Gandalf and Tom Bombadil might very well be "the last of the breed" in Gandalf's reckoning, and as such would be one of the few with whom he could share the old stories.
2 FWIW, his Sindarin name Iarwain Ben-adar (Eldest and Fatherless) is another point to him being the first being on Middle Earth as we know it.
The suggestion that Gandalf was visiting Tom Bombadil to speak with the "Master" is the most logical one. As he says to the hobbits upon their parting company: "I am turning aside soon. I am going to have a long talk with Bombadil: such a talk as I have not had in all my time." This points to the importance of the meeting, and the heightened status of Tom, at least in Gandalf's mind. Gandalf now feels, following his death and rebirth and the defeat of Sauron, that he is able to talk with him like never before. His negative comments in regard to Bombadil at the Council of Elrond may need, in his mind, to be readdressed. This adds to the argument in regard to Tom Bombadil being a manifestation of Eru.
There's also the theory to consider, that Tom Bombadil was some kind of aspect of Iluvatar; a way to have a perspective in the world without interfering himself. This means it could be just a report on the situation to his superior.
The power of Tom Bombadil had no match. The ring was a thing so complex, so powerful, that were none in the world able to undo it, or even completely control it (except for Sauron in this regard). None but Tom. Tom could not be corrupted by the ring, could not be controlled or tempted. Even more impressively, he could change the ring, control it, play with it in a technically impossible way.
So I always imagined this talk between him and Gandalf as a discussion about "Is the work really done now? What is left to do? What are the possibilities for the future; is it really rid of Melkor and Sauron's influence for good?". Should I stay or should I go now?