What convinces the soul to come back and stay in the body? When the person goes against their nature and takes the vile tasting medicine, the soul understands that it is within the person's ability to break their nature. This gives the soul renewed hope that the body might yet break its nature in order to serve God, and so it agrees to stay in the body.
Some people hear this and think, oh, so now when someone is sick, it means they're a sinner.
I hear this and think: Wow, the world is more beautiful than I thought, illness isn't for nothing.