To help Rey understand, Luke takes her back to the origins of the Force itself.
They see two children playing near a tree on an alien planet. The boy noticed that he had greater strength and intuition when he was closer to this tree. The girl noticed that the tree also made her brother increasingly angry. One day an argument breaks out between the children, and the boy kills the girl. The boy touches the tree and is “transformed.” He kills his parents and leaves the planet. Meanwhile the girl is revealed to be alive, transformed by the tree as well, using her power to start the first Jedi Order.
So, humans first encountered the Force via a tree on a planet far, far away. Intriguing. But what’s more intriguing is the fact that this girl tells her followers that she will be reincarnated, as a boy or a girl, millennia after her death. I think we all know where this is going.