some notes on why erick got chosen for his role:
basically, the role of The One To Slay Chaos Incarnate had three requirements: firstly, had to be a sorcerer. the greater deities outside of reality itself have a lot of trouble being able to communicate with anyone who isn't a sorcerer. erick was already a sorcerer.
second, having or being likely to gain an unnaturally long lifespan. the preparation for their role is gonna take multiple regular lifespans and must be undertaken by one individual. erick was determined by the particular deity that selected him for the role to be highly likely to manage that, and they were proven correct.
finally, a high level of learning capability for the arcane. erick was already in the possession of a particular artifact that made this practically a moot point.
while erick was the one chosen for the role, it was not guaranteed that he would be. many other candidates existed, he just so happened to be the one picked, seemingly at random.