having good behavior among the nations, so in that which they speak against you as evil-doers, they may by your good works, which they see, glorify God in the day of visitation.

 It was by no means only menial tasks which were performed by slaves. Doctors, teachers, musicians, actors, secretaries, stewards were slaves. In fact, all the work of Rome was done by slaves. Roman attitude was that there was no point in being master of the world and doing one's own work. Let the slaves do that and let the citizens live in pampered idleness. The supply of slaves would never run out. 