A first idea about how and why changing the past.
Prophecies as result of Time Travel
Fiction can help us to get an idea of what is necesesary to create prophecies in the past. What would be needed to create for instance prophecies like those in the bible? Lets take the example of future scientists that have a broadcasting device that is capable of sending messages through time.
To keep things fairly simple we presume that true prophecy does not exist in the history of these future scientists. Their world is therefore different to that of ours, as in our history there are many recorded works of prophecy. The lack of having historic records causes these future scientists to have a more positive tendency towards sending explicit predictions to the past.
Since in the world of the decision makers there is no evidence that sending messages to the past can change history and no proof that their own past has ever been changed by prophecies or anything that might hint at time travel, they might conclude that experimenting cannot change their present time. Therefore they will not be worried about the consequences of sending explicit prophecies.
The main objective of the future scientists makers might be to make the world a better place. They try to do that by changing the way people think and behave. Because of the anticipated good such a project might bring, any collateral damage caused by the project will be seen as acceptable. The content of the message is firstly meant to convince the prophet and his contemporaries of its importance. Prophecies can convince as no other type of message that it is of supernatural origin. A quick acceptance improves the chances of spreading the message to a large public.