Final answer:
Sauron must not regain the One Ring because it would restore his full power and enable him to spread evil across Middle-earth. The only way to stop him is by destroying the One Ring in Mount Doom. This reflects the philosophical questions of morality, power, and the persistence of goodness in the face of absolute corruption.
Step-by-step explanation:
It is critical that Sauron not regain possession of the One Ring because the ring contains a significant portion of his power, and if he reclaimed it, he would fully regain his power, leading to tyranny and destruction across Middle-earth. Destroying the One Ring in the fires of Mount Doom, from whence it came, is the only method to prevent Sauron from acquiring it.
The task is fraught with peril because Sauron's forces are constantly seeking the ring and the journey to Mount Doom is treacherous. Thus, the Fellowship embarks on the quest to destroy the ring and ultimately stop Sauron. The presence of an all-powerful entity like Sauron in possession of the One Ring raises philosophical questions about the nature of power and morality.
This scenario parallels the problem of evil in philosophy, reflecting on whether an omnipotent and benevolent deity can coexist with evil. In the context of Middle-earth, the power of the One Ring and the potential for absolute corruption underscore the difficulty of balancing power with moral responsibility.