The best way to look at this text is from a psychoanalytic perspective. First, you must choose an approach - Freud, Jung, Maslow, etc. Camus is probably best investigated through a Freudian reading. Quite simply, the ego and superego are almost completely lacking. Meursault seems to have no remorse, no sense of empathy, no compassion, no sympathy for anyone. His mother's funeral is another event he must attend. The weather takes on more importance than giving his regards to his own mother. Thus, from this we can observe a complete focus on his id - mere pleasure.
What is ironic is that through this text's focus on merely id, without regard for ego or superego, we see the error in Meursault's ways. Because of Meursault's lack of morality, we are inspired to respect morality. Very clever.
The protagonist, Meursault, refuses to justify himself to the other characters and the reader. By narrating the story through Meursault's indifference, the reader is drawn into his point of view, feeling the absurdity of the events. The structure of the story also adds to the theme of absurdity. In the first part, Meursault's normal routine disrupts into chaos when he kills the Arab. The second part shows how the law brings back order through Meursault's death.
Everything is meaningless to Meursault. Neither religion nor fate can offer an explanation for the senseless acts of humans, such as murder and war. The alternative is absurdity, the "truth" that life is meaningless. Meursault is convicted not only for murder but also for his psychological indifference, his selfish behavior, and his uncaring insensitivity to his mother's death. He dies because others hold on to their illusions. He says, "...I was sure of myself, sure about everything,...sure of my present life and of the death that was coming. That, no doubt, was all I had."
Camus also shows that human life is meaningless because the only sure thing in life is death. Meursault realizes that the universe is indifferent to him because he will die and have no other importance. The irony is that Meursault is able to be happy only after understanding the meaninglessness of his life. He's now free to make the most of his remaining days. He accepts the reality of his impending death.