The human being
The human being is an animal who is embedded in an experience that far surpasses his ability to fathom or understand. According to Freud, the result is that the animal nature of a human causes that person to desire a religious experience, so that they can function meaningfully in a world that perplexes them. The religious experience of a human is an elaboration of their various mechanisms for seeking meaning. Just as the love of a parent brings meaning, the human can participate in meaning systems that make God into a loving parent, but Freud argues that this is just an illusion of their consciousness.
God
Freud doesn't argue in this book that there certainly is no God, but he does argue that the human experience of communing with God is certainly an illusion of the human conscience. The God of human imagining is an archetypal phenomenon of the human consciousness, he argues. Freud says that what humans experience of "God" is really their desire to make sense of a complex reality through the lens of their character-psychology. We make God into a human character because that is what our minds perceive.
The Oedipal man
The story of Oedipus gets an important shout out in this story. The story is from Greek mythology, and basically, the story is about a prince who accidentally assassinates his father and beds his mother to become king. The story can be seen as an elaboration of a psychological experience of reality that Freud explains here; he says that a person's willingness to view God as a personal parent-figure can be seen as an Oedipal experience of existence. To make God into a parent who can protect and provide is to express a desire for parental protection; it is a projection of the Oedipal complex onto God, says Freud. This is the "illusion" in full bloom.
