Have you ever actually read the original writings of theosophists and gnostics? They talk about how everything is a manifestation of God, how there is only one God, etc. How can that be different from the monotheistic god of any of the religions?

In gnosticism there is this idea of a "demiurge" yaldabaoth which created our physical universe to use the beings within as slaves. That isn't the god of the universe, and I also don't recall the idea of Lucifer being present in the old gnostic texts. I think Luciferians believe that with knowledge of natural law they can take advantage of others so that they can "rule in hell" rather than "serve in heaven" because they view natural law as a prison. But I wouldn't lump all Theosophy and Gnosticism in with Luciferianism. Also as far as I know, Theosophists don't agree with the gnostic idea of this realm being created by a demiurge; they see the physical realm as being a place necessary for the soul to learn lessons and grow in knowledge and ability so that it can expand to ever higher vistas of knowledge and experience through subsequent incarnations.