The king became very angry at the unforgiving slave. So he called him, and said: ‘You bad slave, did I not forgive what you owed me? So, should you not have been forgiving to your fellow slave?’

He should have learned a lesson from the good king. But he had not. So now the king had the unforgiving slave thrown into jail until he paid back the sixty million pieces of money. And, of course, in jail he could never earn the money to pay it back. So he would stay there till he died.

Matthew 18:21-35.