Saul was out to find Christians and punish them for their faith. Saul has hurt many Christians in Jerusalem and now he has received the approval of the High Priest to travel to Damascus to hurt more Christians and bring them bound back to Jerusalem.
 As he was traveling, it happened that he was approaching Damascus, and suddenly a light from heaven flashed around him; and he fell to the ground and heard a voice saying to him, "Saul, Saul, why are you persecuting Me?" And he said, "Who are You, Lord?" And He said, "I am Jesus whom you are persecuting, but get up and enter the city, and it will be told you what you must do." The men who traveled with him stood speechless, hearing the voice but seeing no one. Saul got up from the ground, and though his eyes were open, he could see nothing; and leading him by the hand, they brought him into Damascus. 
If your a Christian you are a child of God. When a Christian is persecuted it is like persecuting God. Saul was not out to persecute God when he persecuted Christians. Saul did not understand or see the good news concerning Jesus. Saul was spiritually blind. Now Saul is physically blind too. Jesus called people that could not see the truth as being spiritually blind. We need to pray for people who are spiritually blind and do not see the truth. In their blindness they may hurt Christians, but continue to pray for them. Only God can open their eyes so they can see the truth and know Jesus as their Lord and Savior.
Acts 9:3-8 (NASB)