Any interpretation of a given work of literature leaves itself open to massive debate, so I can present one of the central ways in which this classic horror story can be interpreted, but please do not let this analysis prevent you from exploring other ways of "reading" this great example of Poe's Gothic fiction.
Key to this analysis is a symbolic interpretation of the events contained within. The story is set during the final days of the Spanish Inquisition, and the first-person narrator hears judges condemn him to death. What he suffers in his prison cell causes massive terror, especially the pendulum, which forces him to watch his death sink lower towards him, literally inch by inch.
These torture methods by some are viewed symbolically, which leads some critics to argue that this short story is really all about a man who dies and almost loses his soul in the pit of hell but is saved by God at the very last minute. Such critics argue that the intense fear the man feels at falling into the pit indicate that it represents hell. The pendulum and scythe represent the time running out for the prisoner and death coming to claim him. The rats that crawl over him symbolise death and decay, as they horrify and disgust the prisoner. Lastly, the trumpet blasts and other apocalyptical sounds eat the end of the short story are strongly suggestive of Judgement Day:
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! The fiery walls rushed back! An outstretched arm caught my own as I fell, fainting, into the abyss.
Such descriptions make us think of the action in deeper, more profound, symbolic terms that help us to see the possibility that Poe could using the sufferings of one prisoner during the Inquisition to talk more widely about the eternal dangers that await us beyond the grave.