As I am going to into fire keeping as a devotional practice of unity among three (but also including Hestia and Hephaistos) primary gods of my household, Apollon and Artemis, and Dionysos, I have been giving much thought of the nature of physical fire as it manifests, and what my relationship will be to it as a firekeeper, as well as how it will be part of my relationship with my gods. So I am going to break this down into talking about each of the gods and their relationship to the fire. The fire itself I see as a physical manifestation of them acting collectively.
Hestia and Hephaistos: These deities actually have very similarly related functions when it comes to their relationship with fire. It is really for this reason that I am not surprised by mystic pairings of them either. I do not see Hestia as the living flame, as I have stated in numerous posts, but rather that which supports and sustains the flame towards a purpose. She is the hearth and the oven (the later of which I will fully admit is more supported by time as a Vestal and understanding of Vesta in association with bread production) and the altar, all through which sustenance passes as caregiver to sustain our relationships and kindred. She is likewise the structure which supports the living spiritual fire/souls/divinities with in as via her association with Olympos, her association with Delphi and each household. She is described poetically in her Homeric hymn as a goddess who locks drip with oil, her very being, rather being described as being of fire, is being which nurses the flame beside which, and around which, she is seated, or even bearing as a blooming branch. She makes it possible to sustain new generations of the oikos, and for the gods themselves to receive the offerings of mortals. This makes her important to the oikos not only for sustaining the living fire within the hearth which is necessary but as a goddess of the oikos itself. Hephaistos too utilizes fire functionally, but rather than being of the hearth/altar/household/etc he is a god of the forge, he bears the blooming fire as his in order to use it to create and manifest new forms. Both are working with creative and transformative manipulation of fire and so fire is theirs under their directions. Hephaistos has a lesser role in my life since I am not a metalsmither or forger (although I have blacksmiths among my ancestors) but he is present and acknowledged as a presence associated with these duties I am undertaking in relationship with them.
Apollon and Artemis: These are the deities who have been inspiring me to work with fire keeping. They are fire deities in what I consider an indirect way. That is to say I consider them hot wind-like deities. While they are not the spark and very nature of the flame, they are part of the flame and give form to its nature. They are the organic and natural controlling force of fire that generates fire to manifest in different forms. A fire may be small and warming, comforting, or a raging firestorm out of control devouring all things. There is a certain close relationship with Apollon and Hestia in particular in which we see is part of the relationship as pertaining to flames, as Apollon and Hestia working cooperatively. Or even Artemis who is often depicted with torches and lamps (and in the case of Diana votive offering of oil lamps was commonly found that have led some scholars to think that there was a link of some kind between Diana and Vesta). As such this explains too why Apollon and Artemis are so enamored with springs and rivers, that the water loving nature of these gods is perfectly complimentary to their hot natures, cooling and delighting them. Their relationship with fire is to give it manifestation in which it sustain life for warmth and food cooking (both of which are paired with functions of Hestia’s manipulation and guidance of fire) and manufacturing (with Hephaistos) but to also be destructive and consuming (as particular to funerary service as associated with Apollon). Interestingly their action on water is similar that they can bring and calm storms on the seas as windy deities, however this seems more towards travel specifically where as fire is more tied to their regular cultus. They give strength and vitality to fire by which manifests in one particular form or another. Likewise fire gives a more physical manifestation to the action of these deities than the less corporeal wind does, it is the vehicle for the most direct and immediate actions for the above addressed, as well as for the creative spiritual fires inspired by Apollon.
Dionysos: I struggled with this one, because while I did acknowledge that Dionysos was linked to the nature of fire and he would be part of my fire keeping service, I was not able to pin it down how this connected for me until it came to me in a burst of inspiration. Potential, divine spark. He is the actual spark of the flame, the raw principle of the fire which contains all the potential for its creative (both procreative and artistic), and destructive nature. He is raw and terrifying as much as he is sweet. Changeable as fire is. The spark of divinity within all things, for which he dwells continuously within and beside each of us through the span of our lives and journey into the next world. He is endlessly both consuming and lovingly tender at the same time, never by nature either one or the other unless through a specific medium of influence.
Thus the unity of these deities in the fire service, because in a way they are very inseparable to me.