"The city clerk quieted the crowd and said: 'Men of Ephesus, doesn't all the world know that the city of Ephesus is the guardian of the temple of the great Artemis and of her image, which fell from heaven? Therefore, since these facts are undeniable, you ought to be quiet and not do anything rash.'" NIV translation
The city official calmed the crowd by reminding them of the fame of their city. The city was actually quite proud of their idolatry and was famous for it. We may say that it is just crazy for a city to be proud of its sin but the same thing is as true today as it was back then. There are cities that are even nicknamed "sin city" but, just as God worked in Ephesus, He can do a major work in our sin cities as well.
"You have brought these men here, though they have neither robbed temples nor blasphemed our goddess. If, then, Demetrius and his fellow craftsmen have a grievance against anybody, the courts are open and are proconsuls. They can press charges. If there is anything further you want to bring up, it must be settled in a legal assembly." NIV translation
The city clerk realized that the Christians had not done anything wrong and that it was Demetrius that was causing the riot. He reminded the people that they had courts to handle matters such as this between men.
"'As it is, we are in danger of being charged with rioting because of today's events. In that case we would not be able to account for this commotion, since there is no reason for it.' After he had said this, he dismissed the assembly." NIV translation
What a turn of events and an example of how God takes care of his own. Not only did God turn away the anger of this mob seeking to harm his people, but He used this clerk to convict the hearts of the rioters as well.