You're telling me he's been holding onto that book this entire time and he didn't even read it?
He believed in the Fake Moon for all his life, and his belief was shattered by MC
He's scared of the Sun Book because despite all that, he still want to believe in the Fake Moon, that it's all a misunderstanding, that everything will be fine
That's why even after all that, he tried to meditate one more time right before going to sleep in the church, he knows the truth, but is scared to throw away the fake reality he lived in up to now
At least that's how I read it