You can get the book back, but only later ( after gym 5). As for what’s written, here it is:
“With life there is also death. With death, there also life.
On the darkest day of humanity, the world shall shake, houses will burn, people will be killed.
The land shall shift, and innocent beings shall fall between the crevices.
Four darknesses born from man shall reign supreme and create a world in their own likeness.
The balance of life and death shall be shattered.
The balance between light and dark shall tip.
Snuffed out and destroyed forever. A world born of hatred, evil, jealousy and prejudice.
Disaster shall be the only known hope in the creation of yet another world.”
And here’s the other statue:
” With death there is also life. With life there is also death.
On the darkest day, on the darkest night, tragedy shall befall the Earth.
All those caught in the Lord’s shadow shall be drained and destroyed. The world can be brought to peace again by four lights not born of man.
They shall preserve and save the land, and break down the establishment to single layers of sand.
Light shall once again be restored to the world.
Prosperity and peace shall mesh in one giant swirl.
And the land shall be guided by a new light, the strongest of the four lights.
To rid this world of everlasting evil and blight.”
Also, the Pokemon you could have gotten, Gothita, can also be obtained later (after the eighth gym).