Word has it that the Book of Eternity possesses vast and far-reaching power. Any person in possession of this book, so the tale goes, would have the ability to manipulate time itself. The power of eternity, which is supposed to be contained in the book, would enable its possessor to control space and time as they like. With such a capability, one may alter the course of history and even resurrect the dead.
The Book of Eternity is a powerful tool, yet it carries with it significant dangers. The repercussions of its theft into the wrong hands are terrifying. A single person with such ability may manage and control global events, leading to widespread anarchy and destruction. The planet would be doomed if they used it to free Cronos and usher in a new age of Titan tyranny.
That's why Zeus and the other Olympians agreed to put Cronos and all his power in the Book of Eternity: so he can never threaten their realm again. They understood that hiding and safeguarding the book was the only way to guarantee its power would never be abused. They also realized that if the book were ever discovered, it would be too deadly to leave in the hands of just one person, and too powerful for any human or immortal to resist.
The Book of Eternity's immense power is both a boon and a bane. It can do immense good, but it can also do terrible things if it falls into the wrong hands. Because of the danger it poses to the world and all life, it must be kept secret and safe.
The Olympians have agreed to keep the Book of Eternity hidden and secure in order to prevent it from ever being utilized for time manipulation, which could lead to a paradox and ultimately the destruction of the world.