You might want to think about the theme of salvation and deliverance that runs through this excellent short story of terror and torture. Some critics have argued that this story is an allegory about a man facing eternal judgement and having to choose between heaven and hell. Certainly, if you interpret a number of the features of the story symbolically, this view can be supported by apposite quotes. Consider the terror that the narrator feels when confronted with the pit. He is so terrified of this pit and falling into it that he does anything he can to avoid it:
Shaking in every limb, I groped my way back to the wall; resolving there to perish rather than risk the terrors of the wells, of which my imaginatino now pictured many in various positions about the dungeon.
This fear suggests that we can view the pit symbolically as representing hell.
Secondly, we can view the end of the story, with the coming of General Lasalle, as symbolically representing Judgement Day. Note the sounds that are presented as accompanying the narrator's freedom:
There was a discordant hum of human voices! There was a loud blast as of many trumpets! There was a harsh grating as of a thousand thunders!
Note that we associate Judgement Day with the sound of trumpets and human wails. Clearly, it could be argued, this similarity at the end of the story supports the overall theme of salvation that can be viewed as a symbolic theme of this excellent story.