I think Job was sincere in his belief that he had done no sin and he couldn't think of any way he could have been different. His friends had answers to why Job had problems while Job did not. He didn't agree with them and said that while God was someone to be trusted he still wanted to ask Him why these things were happening,. He was totally committed, but not silent--not ready to go quietly into that dark night. He didn't react to God, he confronted Him. Nothing is so dangerous to a committed believer as the certainty of being in the right. I don't even think that God was mad at him for standing up and demanding an answer. I think God was a little amused, but He gave Job an answer by asking some tough questions which gave Job all the answer he needed. Until Job could fathom the power and the ways of the Almighty, he would have to be content with the knowledge that those ways were just and loving and would bring him through it all even if he didn't see or agree with the why.