The following are some rough, underdeveloped notes attempting to connect some different aspects of Gandalf’s character, history, and peculiar mission and practice in Middle-earth. The first datum comes from Tolkien’s long letter to potential publisher Milton Waldman describing one of the central “motives” in The Lord of the Rings:
Here [in the story of Beren and Lúthien] we meet, among other things, the first example of the motive (to become dominant in Hobbits) that the great policies of world history, ‘the wheels of the world’, are often turned not by the Lords and Governors, even gods, but by the seemingly unknown and weak—owing to the secret life in creation, and the part unknowable to all wisdom but One, that resides in the intrusions of the Children of God into the Drama…” (Letters 149, emphasis mine)
So the first reference point for the present discussion is the central theme in Tolkien’s work of the small, the unknown, the unobtrusive, and the weak—animated by a “secret life in creation”—being responsible for accomplishing things not possible or anticipated by the strong, the noble, and the great.
A second point is that this “secret life in creation” by which “the One” unexpectedly and eucatastrophically intrudes himself and his purposes into the world sounds a lot like the Secret Fire or Flame Imperishable which Ilúvatar in the Ainulindalë, to the surprise and joy of the Ainur, sends into the Void to burn at the heart of the world, “kindling” it into its very existence. And though the Secret Fire is not mentioned by name, I think we see something of its distinctive agency in the vision Manwë is treated to in the chapter “On Aulë and Yavanna”:
Then Manwë sat silent, and the thought of Yavanna that she had put into his heart grew and unfolded; and it was beheld by Ilúvatar. Then it seemed to Manwë that the Song rose once more about him, and he heeded now many things therein that though he had heard them he had not heeded before. And at last the Vision was renewed, but it was not now remote, for he was himself within it, and yet he saw that all was upheld by the hand of Ilúvatar; and the hand entered in, and from it came forth many wonders that had until then been hidden from him in the hearts of the Ainur. (Emphasis mine)
This characterization of the Secret Fire, taken together with the first point, suggests that the above theme of the weak doing great things on behalf of the great is something of a signature or trade-mark activity of the Secret Fire. Beyond merely bringing the world into being (or rather, precisely on account of it), this is the kind of “business” that the Secret Fire is in, the kind of work that the Secret Fire does.
A third point is that, as is well known, it is this same Secret Fire whose servant Gandalf identifies himself as when facing down the Balrog on the Bridge of Khazad-dum. Assuming for the moment the principle of “like master, like servant,” we are led to the conclusion that it is this same line of work that Gandalf also specializes in, the paradoxical business of accomplishing mighty deeds through comparatively weak, insignificant, or overlooked means. (Tolkien’s indication in an interview with Clyde Kilby and elsewhere that the Secret Fire is the Holy Spirit would seem to further identify Gandalf as something of a Pentecostal, but I digress.) It is also interesting to note in this context Tolkien’s particular choice of words in one letter to explain why it is that Gandalf ultimately never has to personally fight and overcome the Lord of the Nazgûl: “so powerful is the whole train of human resistance, that he [Gandalf] himself has kindled and organized, that in fact no battle between the two occurs: it passes to other mortal hands” (Letters no. 156, emphasis added). As the protégé of the Secret Fire, Gandalf’s apostolic ministry (something I comment on elsewhere) involves him in going about and “kindling” fires among the Children of Ilúvatar, the unexpected but necessary consequence of which is that it is a mere shieldmaden of Rohan and her Hobbit-thain who together slay the Witch King whom no man is said to be able to kill.
Fourth and lastly, knowing this about Gandalf helps explain in part his attachment to and involvement with Hobbits, in whom Tolkien says above that the theme of the “great policies of world history” being accomplished by the “seemingly unknown and weak” comes to be particularly manifest. Enfranchising and fellowshipping with Hobbits, in short, is “Secret Fire” work, something that helps round out Gandalf’s already christological typology: if you’ve seen Gandalf, you’ve seen the Secret Fire who sends him.