What is the theme in Barabbas by Par Lagerkvist?

The quest for faith is the main theme. Barabbas notes from his first meeting with Jesus that there's something different about Him. As Barabbas notes, it's evident that Jesus is innocent of any crime and that he doesn't deserve his sentence. When Barabbas leaves Galgotha and goes into Jerusalem, he's quiet and his friends note that he's not himself. First, he talks to the hare-lipped girl. She's surprised that he stoops to talk to her. Then, he gives her part of his food and is reserved with his friends. He eventually tells them that he saw a glow around Jesus before he was taken to be crucified and the friends say that it was a trick of the light because Barabbas had been in the dark dungeon so long. He says that it turned dark on Galgotha and they again put it down to his eyes.