Acanthio dreamed of becoming a Knight of the Holy Golden Empire. He trained his mind and his body for years to that end. But when he applied to the Army, his request for Knighthood was rejected, and he was instead put into the Mage Division. Now, he'd never have a chance at being a Knight.

But the Priests say that when God closes one door, he opens another.

It's just that, usually, it's assumed God will open a door that's from within the world. Not from outside of it.