The narrator of the novel has a problem. His life, which fits the American consumer-type ideal, is leaving him sick and struggling to sleep at night. In fact, the only way he can sleep at night is to go to support groups for people dying of cancer and other terrible diseases. By "losing all hope" the narrator finds freedom and a release from the pressure and insanity of his job where he makes calculations about auto recalls depending on how much it will cost and how many people will die.
Once the narrator meets Tyler Durden, he sees a way past all the trappings of this consumer-driven lifestyle and eventually begins to work with Tyler to plot to bring down the whole system. The rush they both find in "fight club" has to do with real life, with something that isn't driven by the need to consume or controlled by the media or a profit motive. It is a real sense of being alive and fighting for your life, a place where all these men find an identity that they cannot find in their empty lives.
As they form the Paper Street Soap Company and fill the house with their recruits, the novel's commentary on consumerism and capitalism becomes even clearer. Their mission isn't to make soap, it is actually to subvert capitalism and consumerism in any way possible.
Through the narrator's and Tyler's actions and their conversations, the novel points out some of the emptiness of both capitalism and consumerism. Both complement each other but only in a temporary, unsatisfying way. The idea that owning more things leads to fulfillment is decried throughout the novel.