Question

Sometimes, you read a book and it fills you with this weird evangelical zeal, and you become convinced that the shattered world will never be put back together unless and until all living humans read the book

Answer 1

This is a quote from John Green's "A Fault in our Stars".

It's basically an exaggeration depicting the emotion of a reader who has just read a book that made a very strong impression on the person to levels that he wants everyone to read this book so as to feel the emotions that swell within John. This want is depicted by the phrase "weird evangelical zeal". The reader acknowledges that such a zeal is weird. Few things can make a person want to scream a message to the whole world which is the emotion the above exaggeration is describing. John simply desires for everyone to feel what he felt, but he knows it's most likely not possible to carry another person on the ride of intrigue he experienced, hence admitting that it is weird. There's an irony there because he knows it would be difficult for another to convey theirs to him too.

The exaggeration continues when the John declares that the world stands a chance of fixing itself only after it has read the book. Here John is simply implying that reading this book would be helpful to every reader in every circumstance.