In my fantasy world there exists a book that contains everything that has, is, and will happen as well as every emotion, thought, and action. This book is known as the Acabar.
One cannot physically "read" this book instead one asks the book a question and the book tells them the answer. The book is even able to open and project a "body" for itself, but also display images.
As expected this book has become a site of pilgrimage and is kept in a temple for safe keeping. Pilgrims from across the known world come to ask the book questions and receive answers.
However the priests have noticed one thing: whenever someone asks about the present or past, the book's explanation, while long winded, is clear and easy to understand. However when someone asks about the future the answer is rather confusing and hard to grasp. A example would be taking a book like The Hobbit and seeing how easy it is to understand and then reading Revelations (the biblical Revelations) and comparing how difficult parts of Revelations are to grasp.
Here's an example of descriptions from the two books. First The Hobbit:
In a hole in the ground there lived a hobbit. Not a nasty, dirty, wet hole, filled with the ends of worms and an oozy smell, nor yet a dry, bare, sandy hole with nothing in it to sit down on or to eat: it was a hobbit-hole, and that means comfort. It had a perfectly round door like a porthole, painted green, with a shiny yellow brass knob in the exact middle
Now a description from Revelations:
Then, a Beast emerges from the Earth having two horns like a lamb, speaking like a dragon. He directs people to make an image of the Beast of the Sea who was wounded yet lives, breathing life into it, and forcing all people to bear "the mark of the Beast", "666". Events leading into the Third Woe:
While the description from The Hobbit gives a clear image of at least the door saying it's round, "like a port hole", and green. While the description from revelations, while having parts that can be imagined, others that are open to interpretation/wildly different depending on who's reading.
So why would the Acabar be able to explain the past and present in a clear and easy enough (it can still be wordy and confusing for some) manner to understand, but when explaining the future it's hard to understand what The Acabar is trying to explain or trying to make sense of the imagery and descriptions it is using.
by Revelations I mean the descriptions mainly. For example how Revelations describes the beast, or the four horsemen. The Acabar would answer in a very similar, cryptic and metaphorical, tone.
When The Acabar tries to display images of the future they are not as clear as images from the present. Ex: "From the east will rise a red beast with four arms with a flaming sword in each hand" it will depict exactly that even if the person asking the question is unable to grasp what the Acabar means by this (better put: the image will appear how the person would see it not what The Acabar is trying to describe)