One of the things for which Ephesus was famous was an enormous coliseum that sat 25,000 people. At first this open-air coliseum was used for theater productions, but later it was used for gladiator events. So in his analogy, Paul might have been likening the believers in Ephesus to gladiators. Or Paul might have been likening the believers in Ephesus to Roman soldiers. Both gladiators and soldiers were professional fighters.