What do you see as the lesson or moral of "The Guest" by Albert Camus?

Albert Camus's "The Guest" details the story of Daru, a French-Algerian schoolteacher who is stationed in an isolated mountainous area of Algeria. After Balducci, a Corsican gendarme, arrives at the schoolhouse dragging an Arab prisoner behind him, Balducci informs Daru that the Arab man has killed his own cousin with a billhook over an unpaid debt of grain; Balducci demands that Daru host the man overnight in his home so he does not escape and then escort him the following morning to the police headquarters in Tinguit. Daru has no interest in performing these duties, but Balducci forces the responsibility upon him anyway.

Although initially suspicious of the Arab man, Daru eventually develops a sort of strange and unwanted sense of brotherhood with the stranger:

Men who share the same rooms, soldiers or prisoners, develop a strange alliance as if, having cast off their armor with their clothing, they fraternized every evening, over and above their differences, in the ancient community of dream and fatigue.

In the morning, Daru brings the Arab man to a fork in the road, offers him food and money, and presents him with an option: he may walk the two hours to the Tinguit police administration and turn himself in or he may flee across the plateau to take refuge in the pasturelands with the first nomads. The Arab man chooses to turn himself in, and Daru returns to his classroom alone, where he scrawls, "You handed over our brother. You will pay for this," on the chalkboard and surveys the landscape "he had loved so much" in deep isolation. 

Many critics regard this story as a metaphysical examination of the dilemma of human existence and the many moral quandaries that come with it. In the story, Daru is faced with holding the future of a complete stranger in his hands: does he condemn this man to a life in prison (or execution) despite only knowing his crime and not the context of it or the life of the man who committed it? Or does he set the man free in spite of the fact that the man took another human being's life? It is an impossible choice, and, thus, he chooses not to make it, giving the Arab man agency over his own life. Still, almost unreasonably and without true explanation, the Arab man submits himself to the forces of the law. This conflict is ultimately a question of the sometimes opposing forces of justice and freedom.

The story doesn't necessarily have a "lesson" per se, but it does bring up moral questions which the reader must consider for him- or herself. The power dynamic at play here shifts and is perhaps a reflection of the colonialist politics of the time in which an invading force unhinges the way of living in a different land. By the end of the story, Daru has had to confront his isolation, the cruelty of the situation in which both he and the Arab were placed, and the unfathomable ties that bind members of the human race who are inevitably destined for death.