Acts 9:4 He fell to the ground and heard a voice say to him, ‘Saul, Saul, why do you persecute me?’
Saul was doing what he thought was right – he was following the what the chief priests and others were saying – he was quite sure he was right in doing so!
God knew Saul’s heart and stepped in to stop him from blindly following the rules because God wanted him to listen.
Saul was too adamant in doing what he was doing to stop and listen for God; so God stepped in and made him stop!