Not seeing is no reason for not believing. Nobody sees radiation. We wait for its effects. Nobody sees God, but millions find the effects in their lives. Unexpected and miraculous things sometimes happen—things that can only be from Him.
A certain well-known evangelist was attending a convention in Indianapolis about mass evangelism. Inspired by the stirring messages he was hearing about winning the lost, he went with his song leader to the street corner during an intermission that evening...
God seldom speaks to strangers who have no time for Him, and even if He did, they would not recognise His voice. He loves to speak to people who love Him...