There are chosen souls in the universe who transmit their wisdom and experiences. These souls have allowed humanity to evolve through the different eras of its existence helping to transform humankind and thus enabling those they have accompanied to transcend.
In many cases, these entities may not have needed to return and experience a physical life. But they were and are essential in showing and teaching how to transcend the limits that beings have had in each era and place.
Each of us, in turn, is gradually learning to be in this place and thus be able to fulfill the mission that we are called to in this life.