The question of the book's title is a little self-aggrandizing, but one could argue that Freud earned it with these arguments of religious philosophy. By stripping the religious considerations of any belief or credence, the book takes a new hypothetical point of view; what if what humans experience as religion is simply the human animal demonstrating its various psychological capabilities, applying mental processes to the problem of existence?
The illusion is shaped this way; a person desires control and understanding in an experience of reality that far surpasses their understanding or control. Therefore, their mind gets to work, attempting to find meaningful patterns in reality, and discovering through projection that there is a religious experience—but Freud says that it is just desire for wish-fulfillment. The frustrated person wants to go back to the Oedipal comfort of union with the mother, and so they project onto reality that there must be a God whose role in relationship to humanity is paternal and parental.
This is the psychological experience of religion, described through psychological language. The question then becomes, what is to become of religion now that a human being, namely Freud, has unraveled the mystery? This is where a wise reader might contrast the writings of Jung about the same subject, because to Jung, the experience's obvious religious shape actually implies that their might be a God who designed this reality to make humans desire God in a particular way; Freud's Future admits this, however. He admits that technically, the question of God's existence is still up for debate; he says it is a non-starter, and it is, but technically, the Future is as mysterious as the present. Who knows how to make sense of this reality we all share? Understanding the illusion certainly helps, in any case.
