To me, the Black Flame is roughly the Luciferian analogue to Crowley’s True Will. There are important differences, but at 10k feet, it is a useful shorthand comparison for an explanation.
It is the individual divine spark: the truest core of the self. To fan the Black Flame is to learn, forge, refine, and become more fully what you are. In that sense, it is part of the process of self deification.
For me, the Black Flame is my fire, my stance, the shape of my fire before voice is added to it. It is the core essence from which my choices and actions emerge.
The work is to find it, strip away what is not truly yours, forge what remains, and live in alignment with it. In other words, it is not merely a technique or temporary state. It is the path, and ultimately the life.
Your explanation might be different. This isn't an official explanation of Luciferian theology, just a quick reply. Im pretty tired so this is what ya get for now.