Al Chem , the root of Alchemy is a science developed by early Egyptian and Arabic philosophers and scientists. The proposed to make lead or "base" material turn to gold or "refined essence" by a process of transmutation. There are many steps in this process and it may be seen as the esoteric section of chemistry and physics, the spiritual principals behind each. In the tarot each card represents an aspect or process of this science called Alchemy.
The card THE DEVIL, is the key to Coagulation. Why? because the state of the androgyny isn't possible within and creates a duality that is debilitating when it comes to our goal. Before i discussed some of the ways this key led to Error and Illusion. However there are some benefits to the card as well ( please dont' mistake this following post for satanism, its not!)
The benefit is that our Key shows us the result from one-sidedness, it shows us the error that as long as we are rejecting one side of consciousness for the other we are in total separation of that consciousness from the creation of our androgyny. meaning that we are creating duality and we resolve it as well. This is the meaning of solve and coagulate. Solving is the working out of the image like we are doing, and coagulate is the crystallization of the process into an image or seed-idea.
This may seem boring and irrelevant but its not. Much of what western psychology works on is the integration of the unknown elements of a psyche through the process of individuation, however when the duality of conscious and unconsciousness is integrated this card is no longer a jailor but a reminder of the goal which is the hermetic axiom "the below reflects that which is above".
In the tradition of the temple, templars aren't working to "get beyond" the material like other alchemical systems. Templars work to transmute the here and now. Just as the Lead contains the Gold , and the dross must be removed to show its quinta essence, so does the human reflect the divine and "the Malkuth or Sovereignty of Godhead is within" us all.
Therefore this card represents what dualistic thinking does and how it separates male and female and creates androgynous beasts. Another correlation is the Secret essence tantra and what Longchenpa Rabjam calls the Great Perfection and that " the mandala of pristine cognition is never separated from cyclic existence".
F.L. Cor Meum Lucidum.