This is another fun card, becasue of its misuse and misunderstanding and is another hollywood faverotie for being the bringer of ill omens.
The Devil represents wild and uncivilized aspects of our psyche that we normally tend to repress. We often fear and feel ashamed of these hidden parts of our nature and choose to disown them. The fact that we are so uncomftrable with our base nature means that we frequently project onto other people, so that we do not have to deal with it ourselves.
This tends to wrek havoc on our lives and casue more problems than if we dare openly to acknolwege all of what we are. When are are able to unlock the parts of our psyche that we find unpalatable, a huge amount of posistive energy is released.
The Devil teaches us to recognize and intergrate all aspects of our nature, bot the dark and the light. He is a reminder that we are all made up of good and bad. If we can accept our human failings then we are likely to be more tolarant of others and ourselves and not project blame.