Great topic brother! This is where I currently stand on it. Keep in mind that this is my interpretation, not an attempt at a universal theory of magick.
It is also important to understand that I work with demons relationally. My practice is less focused on spellcraft and more concerned with becoming, who and what I am being changed into through the work. That distinction matters to everything that follows.
I believe magick works, or at least can work, by changing the practitioner fundamentally from the inside out. Whether that change occurs through work with demons, angels, deities, or the practitioner’s own mind, the result is that the person becomes different. They become more than they were.
Once I change, I begin to perceive the world differently. I make different choices, stand differently, think differently, move differently, recognize possibilities I previously could not see, and respond differently. Because I no longer meet the world as the same person, the world can no longer respond to me in the same way.
This is how I understand Luciferian self-deification: not as becoming a literal god, but as consciously taking responsibility for who and what I am. I choose my values, my direction, and how I move through the world rather than allowing those things to remain unconscious or externally imposed. Very godlike in stance.
It also broadly aligns with Crowley’s view of magick (calm down, I said broadly aligns

) as causing change in conformity with Will. In my interpretation, the first and most fundamental change may be within the magician. As the magician changes, their actions, relationships, circumstances, and experienced world begin changing with them.
There is also a metaphysical or perceptual dimension to it. We participate in a shared reality, but none of us experiences that reality without the filters of perception, belief, memory, expectation, and personal narrative. Change those deeply enough, and the person’s experienced world changes. Their behavior changes as well, and the external world begins responding to those changes.
To me, this is true power: power in stance, thought, choice, and conscious direction. Spirits may teach, challenge, reveal, or assist, but the responsibility for what I become remains mine. Always mine.
So, in a nutshell: magick changes the practitioner so fundamentally that the world is forced to meet them in a new way.