The set of the story is after world war Terminus. The earth suffered major damage because of the radiations. Humans now coexist with Androids.
After reading several chapters of the novel, I wondered why did Philip K. Dick choose to insert android into the story. Why some people are not real people. My theory is that after a war, People are realizing that human "genius" can put human race to the brink of extension. They usually want to forget the pain but don't want future generation to experience the nightmare they have been through. Survivors are traumatized.  Ambition and lust for power destroy what makes us human. Philip K. Dick as for me is trying to draw our attention on what  really matters, what really makes us different from an android and so make us human. Dick is trying to make us, readers think about what are the specific things that define a human being and from the story it's not the human form that counts. In the novel, androids have human's shapes and physical characteristics; they talk and  they even have memories and desires.But its still not enough to be human.  It is hard to tell at first sight whether the creature standing a front of you is actually a programmed robot or a human being.  So Dick emphasizes on a capacity that human should have that robot don't or can't have. The author talks about empathy, the capacity to empathize. Empathy in the novel as for me is the symbol of the real world out of fiction. It is the source of peace, its from a soul and so is humanist.
Androids are like a suggestion by Philip K. Dick on what could make future generations remember the mistakes of past generations and prevent other catastrophe. The confrontation between both oblige human to pay attention to others and so recognize the lack of what we call the "essence" of humanity within a creature and do something about it.