In a sense, the history of man is the story of the struggle between good and evil. All the great religions have recognized a tension at the very core of the universe. Hinduism, for instance, calls this tension a conflict between illusion and reality; Zoroastrianism, a conflict between the god of light and the god of darkness; and traditional Judaism and Christianity, a conflict between God and Satan. Each realizes that in the midst of the upward thrust of goodness there is the downward pull of evil.
Martin Luther King, Jr. (American clergyman, activist, and prominent leader in the African-American civil rights movement)