Existentialist works by Albert Camus such as "The Guest" examine questions about the way we think about the choices that we make in life. The moral in this story suggests that even when we try to refrain from making choices, we are are still, in effect, choosing.
Daru has pointedly chosen neutrality in the social and political struggles between the French and North Africans. As a schoolteacher at a remote outpost, he is able to occupy himself as a teacher living a spartan life and helping people from succumbing to hunger. Thus, he is annoyed when Balducci brings him an Arab prisoner to deliver to authorities. Balducci makes it impossible for Daru to refuse to accept the prisoner, thereby making a choice for Daru that he cannot sidestep. Camus shows how the choices that other people make sometimes direct our own paths through life.
Daru tries to take back a bit of control by turning the choice over to the prisoner. He gives him food, money, and options: walk one direction and hide with nomadic people, or walk in the other direction and turn himself in to the authorities. Just as he made the choice to kill his cousin, the prisoner makes the choice to face his punishment rather than run from it. Still, it pains Daru to know that he played a role in putting the prisoner in the position where he must make a choice. And ironically, Daru's actions are misunderstood by Arabs who assume that he has turned in their brother. Again, this is all as a result of the actions of Balducci and the prisoner, who end up altering the course of Daru's existence.
Camus seems to conclude that if one lives in the world, one can never live a life of neutrality for oneself or for other people.