‘And as they cried out, and threw off their garments, and cast dust into the air, the chief captain commanded him to be brought into the fortress, bidding that he should be examined by scourging, that he might know for why they so shouted against him.'
So they not only cried out but threw off their cloaks, and hurled dust into the air, with the result that the chief captain, fearful of another riot, commanded Paul to be taken immediately inside the fortress. He could not understand what was causing the furore. So he commanded that Paul be examined by scourging.
Scourging was normal with ordinary people who were arrested, whether innocent or not. It was felt that the only way to get the truth out of them was by pain. Here was Paul, already bruised and bloodied from his beatings, and the intention was to rough him up a bit more, simply in order to try to get to the truth. Then if he proved innocent they could let him go. The parallel between Jesus' treatment after His journey to Jerusalem, and Paul's, continues, save that Paul is able to avoid the scourging. Scourging was a dreadful ‘punishment' and would lay bare a man's back. But possibly the centurion is meaning here something not quite so severe.
‘Cast dust into the air.' Dust is regularly used symbolically. When the disciples were turned away from a city they were to cast off its dust from them. Possibly what the crowd are saying to Paul here is that Jerusalem rejects him. He can only come under judgment. This confirms Luke's view that Jerusalem has rejected God by rejecting His servants.