It is clear that this is another key indication of the kind of character that Montresor is as a narrator. The fact that he has deliberately organised for his home to be empty when he brings Fortunato home speaks of the way in which he is a calculated killer and has deliberately planned to have Fortunato murdered. However, note what he says about his servants and how he achieves the emptying of his house:
There were no attendants at home; they had absconded to make merry in honour of the time. I had told them that I should not return until the morning, and had given them explicit orders not to stir from the house. These orders were sufficient, I well knew, to insure their immediate disappearance, one and all, as soon as my back was turned.
Montresor thus seeks to implicitly recognise the human failings of others. He knows that during the time of Carnival, if given the opportunity, his servants would go out and make merry, even if they were told not to. He cunningly uses this understanding of the foibles of human nature to his own advantage, showing his ability to manipulate others and clearly acknowledging his own lack of scruples in doing so. This helps us develop a picture of a character who manipulates others without any feeling of guilt whatsoever so as to accomplish his own purposes.
It should be pointed out that Montresor does not get any respect from his servants. This is because he is poor and probably can only afford to pay them very low wages. In fact, he may not be able to pay them at all on some occasions. He knows that his servants will all leave the palazzo if he orders them to stay, but this does not mean he knows that all servants would behave the same way under the same circumstances. He cannot maintain discipline because he cannot afford to hire good servants. Furthermore, the fact that his palazzo is empty when the servants are gone shows that Montresor lives all alone. It further characterizes him as a lonely, unhappy man. Fortunato, on the other hand, has a wife and a houseful of friends, relatives, and servants. This detail of Montresor's absent servants does double-duty, like so many details in Poe's story, and shows the author's economical use of words. It establishes that the house is empty, so that Montresor doesn't have to worry about anyone seeing him bringing Fortunato home, and it highlights Montresor's poverty and fallen social position. Even his own servants do not respect him because they know how he lives. They know he can't fire them because he couldn't afford to hire any others. Montresor is not planning to murder Fortunato because he is jealous of him, although this certainly doesn't make him any better disposed towards the man; he has suffered a "thousand injuries" at the hands of Fortunato, and these injuries probably have to do with money. The two men are competitors in buying and selling luxury goods such as art, jewelry, and fine wines, and Fortunato has probably injured Montresor by outbidding him in purchases. Fortunato is mainly interested in the Amontillado because he is hoping to buy a big quantity, perhaps a whole shipload, for resale, whereas Montresor could only afford to buy one cask.