The pace up significantly in book IV. Augustine is now attacking the belief in the pagan gods by mocking their multitude. If they are som many, surely this means that they are very weak. But he gets into som interesting questions here. This is the first mention of the now famous "Augustinan" notion of freedom.
Whatever evils are inflicted upon just men by unjust masters are not the punishement of crime, but the test of virtue. Therefore the good man is free even if he is a slave, wheras the bad man is a slave even if he reigns: a slave, not to one man, but, what is worse, to as many masters as he has vices.I.e. freedom is freedom to do good, not freedom to do whatever one wants.