Heroes. Beings that stand out among the masses and make a difference. They are the pinnacle of human existence, the men and women who have overcome great tribulations to save their world and others from harm. They are still remembered thousands of years after their demises as legends, the people whose stories parents tell their children to inspire them to strive for greatness.
The gods, as childish and selfish as they are, love hearing about them. And watching them struggle to accomplish their goals.
However, there is one entity that appreciates heroes more than anyone else. Unknown even to the puny gods. And that entity is... The World itself. For the World, heroes are like the World's antibodies when an evil that threatens life and the World arises, a hero is born. A being that is able to surpass any limit and destroy this evil.
Now. As a World, would you allow a life form this convenient to just get a mate, an offspring, grow old and die an ordinary death?
No. How illogical. You need to have as many heroes as possible. Why wait for evil to rise when you can just make heroes give birth to more heroes and farm them until their heroic blood gets spread far and wide? In order to do that, though, you need to be able to find heroes. And that is where the human Bell Cranel comes into play. Even when he was still in the womb, the World knew that he was the reincarnation of the Argonaut, a hero so great that even if the gods went against him, he could win.
However, in this Age of the Gods, Greater dangers were born. The Dungeon and the One-eyed Black dragon were the new threats. This time brought by those filthy gods. The World needed heroes like him. Bell would most likely be able to eliminate them, but just in case, the World ought to ensure that Bell's bloodline would not end.
Thus, a blessing had been given to the boy. A huge and throbbing blessing.