Avoiding the Apocalypse, Armageddon
If we continue to deal with nature, science and technology as we have done for the last thousands of years, we might become instrumental in the final wipe out of our own existence. causing our own Armageddon. Therefore it is of utmost importance that as science advances we need to mature our responsibility, conscience, morals and wisdom as well.
Advanced technology definitely needs advanced responsibility and wisdom. Failing to develop and mature these values on time, that is, before we develop critical, cutting-edge technology, might result in putting ourselves in danger of extinction. Future decision makers, being closer to such a tragic, maybe by then, unavoidable event, might think that by sending the right messages back to the past could help to 'mature' humanity in a earlier stage by installing those traits and aspects that are missing by nature. A more ballanced humanity might have better chances to survive and avoid the pitfalls of history.
If you would just change the past a bit, it might not make a lot of difference, life will find a way to make happen what was supposed to happen. If you really want to make a difference you should change human nature, man's way of thinking, acting and behavior from the ground up. Doing so institutes quite a drastic change, something that is impossible to achieve within a single lifetime. It must become an effort of many generations in which the new, 'superior' way of thinking and acting slowly integrates into society and civilization.
It is not difficult to imagine that by creating bibles and religions in the past our ancestors could be schooled in how to unite humanity and overcome differences between people. The purpose of such religion would be to add a spiritual site to humanity and therewith balancing human nature, by doing so Armageddon might be evaded.
If future decision makers really decide that changing the past is an option, then where would they start? Since the improved way of thinking and behavior should spread to as many people as possible, it would be best to choose a moment in the history time line that the human population was still small. The further back in time you would 'plant' a prophecy the more extensive a deviation in history could be achieved. The closer to the cradle of life and civilization you manage to get, the greater the possibility of success in avoiding a future disaster.