At some point the Harbinger accidentally created a method in which he could travel through time, but could only observe events. He eventually developed a way to interact with things, though it took a lot of preparation and power to do so.
The Harbinger had been interacting with the village for some time before 2375 as Turan credited the Harbinger with his existence due to the Harbinger warning the villagers of a particularly harsh winter during Turan's grandparents' lives.
In one future the Harbinger saw he witnessed what he thought was the destruction of the galaxy. To prevent the possibility of this future he resolved to kill a being he dubbed "the Destroyer" in the past.
Travelling back around a decade the Harbinger changed an event on the planet Kobliad that resulted in the Destroyer being shot. Initially the Harbinger believed the Destroyer had been killed as the future was rewritten. However, in a new future the Harbinger saw that the Destroyer survived and would visit his world. Tied to this he also saw the destruction of his temple and the planet.