Job concludes his massive speech in despair because he is only looking at God in terms of the Law, not the Gospel. The grand Gospel statement Job made shortly before was that God would raise Job from the dead and remove his sins from him. When we look to God in terms of the Gospel, we need not despair but find that, although He judges sins, we are not condemned. Although we do not know the future, we know our eternal inheritance in heaven is secure. Through Christ, we have the promise that the Lord delivers us from sin and places us in life.