Keller dismisses the idea that pointless suffering is evidence against God by giving the standard Christian reply that we don't know the suffering to be pointless. God has His ways, and we are not privy to all of them. In the end, we just don't know. I reply that there may be good reasons for all the suffering in the world, but there also may not be. I think that line of reasoning ends in a stalemate.
He also brings up the point that often good comes from suffering. I agree with this statement. In fact, some pain seems necessary for learning, growth, and safety. For example, if children felt no pain when they touched hot objects, they might touch them long enough to be severely burned. We empathize with others more deeply when we have experienced similar suffering, such as the loss of a loved one. There is no doubt that suffering and pain are an integral part of the human experience and that good comes from them.
However, what about suffering and pain caused by God that is not for the inflicted one's greater good? Looking at the Bible we see a prime example: Job. He appears to have been physically tormented, grief stricken, poverty stricken, and reviled by friends all so God could win a bet with Satan. I suppose this gets justified by saying that it was all for the purpose of glorifying God. It wasn't really for Job's benefit as he was already a righteous man. I can't see how Satan would benefit, he seems incorrigible to me. Certainly God has no need to prove himself to Satan or any of us. There is a way in which Job feels like an object to be used by God rather than someone in relationship with God. (Of course, the example of Job assumes a literal reading, which may or may not be the case. Either way, there are other examples in scripture where the reason for suffering is given, though it is not one most of us would deem to be good, if given by the person next door). It's not always the case that we are in the dark about the reasons and motivations of God for causing or allowing suffering.
Next, Keller turns the tables and states that suffering may in fact be evidence for God. This is because declaring something to be evil or wrong assumes there is some objective moral standard upon which to base the judgement. There is a sense in which atheists try to have their cake and eat it too when they deny the existence of God based on evil in the world, making moral judgements based on objective standards which would not exist if there is no God. However, there are those who believe moral standards do exist apart from God, and disagree with Keller's assertion that moral behavior couldn't have evolved. They point to behavior in primates which indicates a sense of fair play, compassion, empathy, and care giving.
Next, Keller addresses the suffering of Jesus at the cross. He points to that moment to affirm his belief that whatever the state of the world, God loves us and suffered for us. Even though Keller doesn't pretend to have all the answers to the suffering in life, he views it all through the eyes of one who knows he is loved and is confident that his best interests are within the heart of God. He also takes heart in the resurrection, calling it a "restoration" of all things. He says it gives us hope, healing all things, and an "infinitely more glorious world" than our present one. For believers, these messages are comforting and one can rest in them, leaving the question of suffering for a chat with God "when we all get to heaven." However, for those who do not believe these things, the matter of suffering still looms large.