As the reader of the conversation we are in a position to assess the conversations between Job and his comforters. With each cycle of conversation they become increasingly aggressive with their accusation that Job is a fool for not recognizing that God is trying to get his attention in regards to some particular sin and turning to him in repentance. Job continues to maintain his innocence and the accusations heighten. The problem is that we know that the friends are wrong because we have been clued in by the introduction. So it is clear to see that the message of the book has some to do with the friends judgment that is based on a lack of understanding about what God is and is not doing in this situation. They have judged harshly, failed to comfort their ailing friend, and do not have access to all the information necessary to understand the situation.
Because of the perspective the reader has been given it is easy to relate to Job in the midst of the accusations saying, "Hey guys, you should probably withhold your judgment, you do not have all the information. If you did, you wouldn't be so quick to impugn his character." By the end of the cycles of conversations it is like the narrative is just provoking us to have this thought, and we most certainly should. It is an awful thing to judge someone before the evidence is in. Our entire legal system in the U.S. is based on the all important principle of "innocent until proven guilty." If there is reasonable doubt we recognize that we should withhold unwarranted judgment.
So is this the message of the book of Job? Most certainly not or the book would end with the conversations between the friends. But the narrative continues and so does the lesson and wisdom. The last section of the book is the conversation between God and Job. In the conversation, which is really two declarations by God, Job comes to find out that he really knows very little about how God created and governs even the simplest things in the natural world. If he cannot understand the simplest things which God has created and governs he can hardly stand and judge the creator Himself in some instance of suffering. You see all along Job has been calling God's character and justice into question and impugning His character. Unfortunately Job does not have all the information about how God governs the world or what in the end he may be up to. He has no footing on which to stand to give him the full perspective of time and space that God alone has. It is as though God is saying, "Hey Job, you should probably withhold your judgment. You do not have all the information or understanding that I have. If you did you probably wouldn't impugn My character." Now I think we are a bit closer to the central message of this remarkable book from the most remarkable library.