"Immediately, something like scales fell from Saul's eyes, and he could see again. He got up and was baptized, and after taking some food, he regained his strength." NIV version
When Ananias was obedient, God's plan was carried out. In this passage we see that the change in Saul/Paul was immediate. When he was touched by the power of Jesus, he was changed. The same pattern should be evident in our lives. When God touches your heart and you accept His grace and mercy, there should be an immediate change in your life. As we see in Saul's case, that change was then followed by an act of obedience (he was baptized). We are all called to the same immediate obedience when God touches our lives.
"Saul spent several days with the disciples in Damascus. At once he began to preach in the synagogues that Jesus is the Son of God." NIV version
In this passage, we see another immediate change in the life of Saul/Paul. After accepting Christ, we are told here that he immediately began to preach the gospel of Jesus the Messiah.
Once again, the same thing should apply to our lives. When you truly come to have a relationship with Jesus Christ, you will share (preach) that good news.
"All those who heard him were astonished and asked, 'Isn't he the man who raised havoc in Jerusalem among those who call on this name? And hasn't he come here to take them as prisoners to the chief priests?' Yet Saul grew more and more powerful and baffled the Jews living in Damascus by proving that Jesus is the Christ." New International Version
After Saul/Paul's encounter with Jesus, his actions changed but people didn't want to believe that he was a different man. Therefore, you get the questions in this passage. The people knew what Saul had been but they couldn't explain what they were seeing now. Not only that, but now this esteemed student of the law was arguing successfully that Jesus is the Christ. Do you have old friends or relatives that see the change in you but do not want to believe it? That is basically the same thing that happened with Saul/Paul. Like him, we are all called to be that example and to speak the truth that Jesus is the Christ even if those around us do not want to believe it. We must trust God to show them and to change their hearts.