At one point in his long essay Freud invents a fictitious opponent who will offer some of the common counter-arguments in defense of religion.

I shall therefore imagine that I have an opponent who follows my arguments with mistrust, and here and there I shall allow him to interject some remarks.

Freud seems to have borrowed this technique from the great German philosopher Arthur Schopenhauer, who wrote a long essay "On Religion" in the form of a dialogue between two men he called Demopheles and Philalethes. Freud's imaginary opponent does not have a name. His most important contribution to the argument is as follows:

The doctrines of religion are not a subject one can quibble about like any other. Our civilization is built upon them, and the maintenance of human society is based on the majority of men's believing in the truth of those doctrines. If men are taught that there is no almighty and all-just God, no divine world-order and no future life, they will feel exempt from all obligation to obey the precepts of civilization. Everyone will, without inhibition or fear, follow his asocial, egoistic instincts and seek to exercise his power; Chaos, which we have banished through many thousands of years of work of civilization, will come again.

Freud’s imaginary opponent does not seem to believe that religious doctrines are true either, but only that they are a necessary part of human civilization. He would probably agree with the ancient Roman philosopher, statesman, dramatist Seneca, who wrote:

Religion is regarded by the common people as true, by the wise as false, and by the rulers as useful.

Many thinkers have expressed the same idea. Those who, like Freud, regard religion as an illusion should not try to influence the masses to share their atheistic views. Benjamin Franklin expressed this caveat succinctly in Poor Richard’s Almanack:

Talking against religion is unchaining a tiger; the beast let loose may worry his deliverer.

Franklin was undoubtedly thinking of the apocalyptic results of the French Revolution, whose leaders did away with the monarchy and the established religion which supported it.                   

And Napoleon Bonaparte once said:

Religion is what keeps the poor from murdering the rich.

As far as the future of religion is concerned, Freud believed that religious belief would gradually wither away but that it would be a long, slow process. Scientific discoveries would continue to undermine religion, and eventually science would take over the role now played by religion in sustaining civilization. He tells his opponent:

It is certainly senseless to begin by trying to do away with religion by force and at a single blow. Above all, because it would be hopeless. The believer will not let his belief be torn from him, either by arguments or by prohibitions.

And a little later Freud concludes with his vision of the future of what he calls the “illusion” of religious belief:

The primacy of the intellect lies it is true, in a distant, distant future, but probably not in an infinitely distant one. It will probably set itself the same aims as those whose realization you expect from your God…namely the love of man and the decrease of suffering.

Freud’s essays make long and sometimes difficult reading. He is not a graceful writer, although he is obviously a deep thinker who is very much concerned about the growing hostility between religion and science. The fact that he was able to publish such a work as “The Future of an Illusion” (1927) seems to prove that organized religion had lost much of its power, while science has gained in prestige at the same time because of the tangible benefits it been able to produce.

Freud calls into question the justifications of religious doctrine. While there have been scientific tests to confirm such a fact that the earth is a globe, Freud suggests that religious doctrine does not allow itself to be subjected to the same kinds of tests. He notes three justifications of religious doctrine: that it was believed by our ancestors, that they passed down proofs to us, and that it is forbidden to question it. Clearly, we do not believe everything our ancestors did; therefore, Freud suggests that religious doctrine should face the same scrutiny. It should not simply suffice to say it is forbidden to question it. 

One of the problems is that religious belief (faith) is not based on reason. It is an inner, personal experience and its proof is in the subjective experience. Freud asks why religious stories continue to be believed (after comparing them to fairy tales). 

Freud supposes that religious ideas are illusions (hence the title) and that people have, and continue to, wish for a religious doctrine (and a God) because they wish for a feeling of protection; the same way a child wishes to be protected by his/her father or mother. 

Thus the benevolent rule of divine providence allays our anxiety in the face of life's dangers, the establishment of a moral world order ensures the fulfillment of the demands of justice, which within human culture have so often remained unfulfilled, and the prolongation of earthly existence by a future life provides in addition the local and temporal setting for these wish-fulfillments. 

Freud concludes that religious doctrine is not an error; rather, it is an illusion. An illusion differs from an error (in this context) in that an illusion manifests from man's/woman's wishes. Freud is clearly skeptical of religious beliefs, even adding the philosophical notions of a more abstract concept of God are equally illusory. Freud's position in this essay seems to be that of an atheist. Freud admits that as religious doctrines can not be proved, they also can not be unproved. But in the end, he sides with reason and sticks to the idea that religious belief is simply a tradition that arose and is sustained by humanity's wish for a sense of divine protection; in other words, an ultimate father figure.