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.
"...in this day and age, it is very dangerous to just simply follow someone. What is best is to seek the Inner Master."