A symbol in alchemy of the sacred fire or Kundalini.
"Sulfur is the fire of Alchemy." - Samael Aun Weor, Treatise of Sexual Alchemy
Since we have lust, pride, envy, etc., that fire is modified, and is called Arsenic (i.e poisonous) Sulfur.
"Let us think for a moment of the humanoid multitudes that populate the face of the earth. They suffer the unspeakable. They are victims of their own errors. If they did not have ego they would not have those errors, nor would they suffer the consequences of such errors. The unique thing required in order to have the right to true happiness is, before all, to not have this ego. Certainly, when psychic aggregates, the inhuman elements that make us so horrible and evil, do not exist within us, then the payment of Karma is non-existent. Thus, the result is happiness."