1. How else are you supposed to bend another person to your will? They weren't skilled enough for mass manipulation, so they used good old brute force and violence.
2. That he's a slave. I guess I would've just tried to run away and take my chances there.
3. It gives him tons of self-confidence. Now he knows he can fight back if he wants to and isn't scared of Mr. Covey anymore.
4. He wasn't just a little slave-boy scared of his master, he has power to resist his master, thus he is a man.