How is the boy able to retain his compassion?

I think the reviewer is right. The boy's compassion seems to come from within. He confounds his father, in the face of such callous cruelty, how his boy can think of others. This compassion runs right through the book. The boy keeps asking the father if they are "the good guys". This becomes more of a lament as the world seems void of any goodness. I think the boy is the last piece of hope in this novel, the last piece of empathy or perhaps even God. One of my favourite lines comes at the beginning of the novel when father says of his son, "If he is not the Word of God, then God never spoke."