In the introductory paragraphs, Freud attempts to understand the spiritual phenomenon of a so-called "oceanic" feeling - the sense of boundlessness and oneness felt between the ego and the outside world. This feeling is "a purely subjective fact, not an article of faith." It does not betoken an allegiance to a specific religion, but instead points to the source of religious sentiment in human beings. Churches and religious institutions are adept at channeling this sentiment into particular belief systems, but they do not themselves create it.
In general, the ego perceives itself as maintaining "sharp and clear lines of demarcation" with the outside world. This distinction between inside and outside is a crucial part of the process of psychological development, allowing the ego to recognize a "reality" separate from itself. After summarizing his previous research, Freud returns to the question of "oceanic" feeling, finding it unconvincing as an explanation of the source of religious sentiment in human beings. Instead, according to Freud, it is a longing for paternal protection in childhood that continues into adult life as a sustained "fear of the superior power of Fate."
In Future of an Illusion, Freud lamented the common man's preoccupation with the "enormously exalted father" embodied by God. The idea of placating a supposedly higher being for future recompense seems utterly infantile and absurd. The reality is, however, that masses of men persist in this illusion for the duration of their lives. According to Freud, men exhibit three main coping mechanisms to counter their experience of suffering in the world: 1) deflection of pain and disappointment (through planned distractions); 2) substitutive satisfactions (mainly through the replacement of reality by art); 3) intoxicating substances. Freud concludes that religion cannot be clearly categorized within this schema.
What does man wish for and aim to achieve in life? Religious belief hinges on this central question. Most immediately, men strive to be happy, and their behavior in the outside world is determined by this "pleasure principle." But the possibilities for happiness and pleasure are limited, and more often we experience unhappiness from the following three sources: 1) our body; 2) the external world; and 3) our relations to other men. We employ various strategies to avoid displeasure: by isolating ourselves voluntarily, becoming a member of the human community (i.e. contributing to a common endeavor), or influencing our own organism. Religion dictates a simple path to happiness. It thereby spares the masses of their individual neuroses, but Freud sees few other benefits in religion.
After looking specifically at religion, Freud broadens his inquiry into the relationship between civilization and misery. One of his main contentions is that civilization is responsible for our misery: we organize ourselves into civilized society to escape suffering, only to inflict it back upon ourselves. Freud identifies three key historical events that produced this disillusionment with human civilization: 1) the victory of Christendom over pagan religions (and consequently the low value placed on earthly life in Christian doctrine); 2) the discovery and conquest of primitive tribes and peoples, who appeared to Europeans to be living more happily in a state of nature; 3) scientific identification of the mechanism of neuroses, which are caused by the frustrating demands put on the individual by modern society. An antagonism toward civilization developed when people concluded that only a reduction of those demands - in other words, withdrawal from the society that imposed them - would lead to greater happiness.
Freud defines civilization as the whole sum of human achievements and regulations intended to protect men against nature and "adjust their mutual relations." A "decisive step" toward civilization lies in the replacement of the individual's power by that of the community. This substitution henceforth restricts the possibilities of individual satisfaction in the collective interests of law and order. Here Freud draws an analogy between the evolution of civilization and the libidinal development of the individual, identifying three parallel stages in which each occurs: 1) character-formation (acquisition of an identity); 2) sublimation (channeling of primal energy into other physical or psychological activities); 3) non-satisfaction/renunciation of instincts (burying of aggressive impulses in the individual; imposition of the rule of law in society).
Even if one of the main purposes of civilization is to bind each man's libidinal impulses to those of others, love and civilization eventually come into conflict with one another. Freud identifies several different reasons for this later antagonism. For one, family units tend to isolate themselves and prevent individuals from detaching and maturing on their own. Civilization also saps sexual energy by diverting it into cultural endeavors. It also restricts love object choices and mutilates our erotic lives. Taboos (namely, against incest), laws, and customs impose further restrictions. Freud reasons that civilization's antagonism toward sexuality arises from the necessity to build a communal bond based on relations of friendship. If the activity of the libido were allowed to run rampant, it would likely destroy the monogamous love-relationship of the couple that society has endorsed as the most stable.
Freud next objects to the commandment "Love thy neighbor" because, contrary to Biblical teaching, he has come to see human beings as primarily aggressive rather than loving. He first identified this instinctual aggressiveness in Beyond the Pleasure Principle, and though his proposed "death drive" was initially met with skepticism, he maintains and develops the thesis here. Civilization is continually threatened with disintegration because of this inclination to aggression. It invests great energy in restraining these death instincts, and achieves this goal by installing within the individual a sort of watchdog agency, which Freud calls the super-ego, to master our desire for aggression. For Freud, the entire evolution of civilization can be summed up as a struggle between Eros and the death drive, overseen by the super-ego.
With the establishment of the super-ego comes a sense of bad conscience. Because it is internalized, the super-ego omnisciently regulates both our thoughts and deeds, whereas prior to its installation, individuals only had to submit themselves to a higher authority for punishment (such as parents) in the case of fully accomplished acts. There are two sources of guilt: 1) fear of authority and 2) fear of the super-ego. In the latter case, instinct renunciation no longer liberates the individual from the sense of internal guilt that the super-ego continues to perpetuate. By extension, civilization reinforces the sense of guilt to regulate and accommodate the ever-increasing numbers of relationships between men. It becomes a more repressive force that individuals find increasingly difficult to tolerate. Freud considers this increasing sense of guilt to be "most important problem in the development of civilization," since it takes an enormous toll on the happiness of individuals.
In the last chapter, Freud clarifies his usage of seemingly interchangeable terms: the "super-ego" is an internal agency whose existence has been inferred; "conscience" is one of the functions ascribed to the super-ego, to keep watch over the intentions and actions of the ego; "sense of guilt" designates the perception that the ego has of being surveyed and arises from the tension between its own strivings and the (often overly severe) demands of the super-ego. It can be felt prior to the execution of the guilty act, whereas "remorse" refers exclusively to the reaction after the act of aggression has been carried out. Finally, Freud re-emphasizes the instinct of aggression and self-destruction as the single greatest problem facing civilization, as manifested in "the present time." He ends by asking which force - "eternal Eros" or his potent adversary - will prevail.