It's an energy field created by all living things. It surrounds us and penetrates us. It binds the galaxy together.
Fear leads to anger.
Anger leads to hate. Hate leads to suffering. Like the story of the Bhagavad Gita, or of Marduke and Tiamat, George Lucas' space opera teaches about the good in all of us, as well as the dangers of evil. His instruction would continue under Yoda and eventually see its completion when he, like Obi-Wan before him, sacrifices his life in order to save another. With literary twists of the plot and the cinematic splendor of the silver screen, Luke is saved by his father, who, in an act of selflessness, turns away from the Dark Side to the side of light.