Balducci brings the Arab to Daru's door, informing Daru that "I have an order to deliver the prisoner and I'm doing so," (90) thus freeing Balducci of the responsibility over wherever the Arab ultimately ended up. Balducci didn't want the responsibility of the Arab possibly escaping, and by doing only as was expressly required of him (delivering the Arab to Daru's door and giving the orders of the Arab's destination to Daru), he was also setting the story so that any decision Daru later took was an act of Daru's alone and was not directly dependent on any other decision another man had made prior. Balducci avoids the social obligation he's supposed to feel. He should follow through on the prisoner's handling, but he doesn't have to. Balducci knows this, and decides to avoid the effort and instead justifies his leaving the Arab there by simply following his orders and not reading between the lines of the order.
After accepting the Arab, Daru was forced to wait for the next day to take the journey to the jail. This presented him with another choice. He could treat the Arab civilly, like a brother, or, he could treat the Arab like an animal (keeping him tied, not giving him a place to rest or a thing to eat). Daru chooses to treat him like a man, even though he didn't see him as one. This impression is also given to the reader, the Arab remains "the Arab," and is not given a name. In the same way we say 'the car,' or 'that dog,' and mean an object identified only by what class of object it falls under, Camus gives us "the Arab," leaving us no option but to see the man as simply a small part of a larger Arab nation, and not as a man with a name and a personality all his own.