The Nexus is the main component of Chronos, it was the single thing needed to complete his complete control over immortality, the dead and the living.
It was a pathway to life and death itself and hoped that Schneider, the smartest man in the world would be the one to accomplish his goal.
But somehow, the Nexus chose Jason and Chronos couldn't understand why because Jason was an insignificant human but the power of the Nexus was unlimited.
There was no barrier or limitations to what one could do once they unlocked it's full potential.
Nexus was not only the beginning but it was the end, an ability that transcended time itself but that went in accordance to what the parasite called itself as it roughly resembled the God of time.