Although he specifically asked for books, none came to mind immediately. Rather, Scripture suggested itself. Two passages stuck in my head when considering forgiveness. The first was from Matthew 18:
Peter approaching asked [Jesus], "Lord, if my brother sins against me, how often must I forgive him? As many as seven times?"
Jesus answered, "I say to you, not seven times but seventy-seven times. That is why the kingdom of heaven may be likened to a king who decided to settle accounts with his servants. When he began the accounting, a debtor was brought before him who owed him a huge amount. Since he had no way of paying it back, his master ordered him to be sold, along with his wife, his children, and all his property, in payment of the debt. At that, the servant fell down, did him homage, and said, 'Be patient with me, and I will pay you back in full.' Moved with compassion the master of that servant let him go and forgave him the loan.
When that servant had left, he found one of his fellow servants who owed him a much smaller amount. He seized him and started to choke him, demanding, 'Pay back what you owe.' Falling to his knees, his fellow servant begged him, 'Be patient with me, and I will pay you back.' But he refused. Instead, he had him put in prison until he paid back the debt. Now when his fellow servants saw what had happened, they were deeply disturbed, and went to their master and reported the whole affair.
His master summoned him and said to him, 'You wicked servant! I forgave you your entire debt because you begged me to. Should you not have had pity on your fellow servant, as I had pity on you?' Then in anger his master handed him over to the torturers until he should pay back the whole debt. So will my heavenly Father do to you, unless each of you forgives his brother from his heart."
I thought about what my friend had said he felt, that in a Christian view, we are punished unless we forgive. So it seems God threatens us to get good behavior. It's possible to read this passage to confirm that, but I don't think that's quite right. One reason comes from Luke 11:
He was praying in a certain place, and when he had finished, one of his disciples said to him, "Lord, teach us to pray just as John taught his disciples." He said to them, "When you pray, say: Father, hallowed be your name, your kingdom come. Give us each day our daily bread and forgive us our sins for we ourselves forgive everyone in debt to us, and do not subject us to the final test."Christians connect our forgiveness of others to God's forgiveness of us. That connection is not simply "if we don't forgive others, God will turn up his nose at forgiving us." If that were true, we couldn't make sense of the unconditional guarantee of love and forgiveness that Luke talks about ("everyone who asks, receives"). Rather, as Christian readers, we're asked to read the two passages together. Then we begin to see that forgiveness is truly supernatural, even when we are the ones doing the forgiving. True forgiveness is like a miracle. True forgiveness (as opposed to a sham forgiveness that forever throws the supposed "forgiveness" in the face of the "forgiven" in acts of perpetual humiliation) may strike us as unnatural or impossible. God is not simply the One who requires forgiveness -- he is the One who makes forgiveness possible, he is Forgiveness and Love itself.
And he said to them, "Suppose one of you has a friend to whom he goes at midnight and says, 'Friend, lend me three loaves of bread, for a friend of mine has arrived at my house from a journey and I have nothing to offer him,' and he says in reply from within, 'Do not bother me; the door has already been locked and my children and I are already in bed. I cannot get up to give you anything.' I tell you, if he does not get up to give him the loaves because of their friendship, he will get up to give him whatever he needs because of his persistence."
"And I tell you, ask and you will receive; seek and you will find; knock and the door will be opened to you. For everyone who asks, receives; and the one who seeks, finds; and to the one who knocks, the door will be opened. What father among you would hand his son a snake when he asks for a fish? Or hand him a scorpion when he asks for an egg? If you then, who are wicked, know how to give good gifts to your children, how much more will the Father in heaven give the holy Spirit to those who ask him?"
So how do we read the passage in Matthew in light of this? To the extent that we are unable to forgive and love, we have not truly accepted God's love -- we have not surrendered our will to His. In the language of Luke, we have withdrawn before knocking, before asking. And that withdrawl of our will from God's keeps us from His Forgiveness, and keeps us from forgiving others.
One of the great Eastern church fathers, St. John Chysostom, delivered an Easter Sermon that contained this passage: "Let no one lament persistent failings, for Forgiveness has risen from the grave." Chysostom identifies Christ as not just forgiving, but as being Forgiveness itself.