Saul was a promising Pharisee. He knew the law inside and out having studied it for years and was quite young to be so knowledgeable. Because of how young he was he was zealous for the cause of the Pharisees and wanted nothing more than to impress. Stephen was stoned to death because of his faith in Jesus and became the first Martyr and Saul was the one who was in charge of the persecution. He went to great efforts to try and cull this sect of Judaism.
With the death of Stephen persecution came to the church and so believers spread out from Jerusalem to escape. Saul decides to take a road trip to the city of Damascus to arrest the believers there. On his way a bright light knocks him off of his horse and Jesus speaks to him. This great display is what is needed to get the stubborn Saul to see that Jesus was in fact the Messiah. Now that Saul knows this all his passion is going to be put towards preaching the Gospel. But first, to humble him, God strikes him blind until he gets to Damascus. He has to stumble his way along.
God comes to Ananias, a believer in Damascus, and tells him to heal Saul when he comes. This is a big ask for Ananias knows who Saul is and knows why Saul was headed to Damascus in the first place. He knows very well he could heal Saul and then be arrested right then and there, taken to Jerusalem, and killed. But God assures him and so he goes and heals Saul of his blindness. Instead of arresting Ananias he was baptized and stayed with the believers in Damascus likely learning about Jesus.
Saul makes his first public appearance in Damascus, which everyone is sure to be expecting a violent affair. They were awaiting believers to be dragged out of their homes and carried off to their deaths in Jerusalem. But Paul stood up in the synagogues and began preaching Jesus as the Messiah. People were shocked. The man who was killing those proclaiming Jesus as the Messiah was and was on his way to kill those in Damascus was preaching the very same message! This was a miraculous event.