So, why did he let satan tempt him? Just because? Or to make a fool of satan? I don't think so. The Book of Job shows that we must never blame God, that those who truly believe will never blame God, that any misfortune and evil does not come from God.
You give us far too much credit that man can somehow overcome our sinfulness to do things that are pleasing to God
The Book of Job gives credit to Job for not giving in to evil, for choosing God in adversity as well as in blessings. Yes, much credit is given to man who is willing to walk in God's footsteps and do good in God's name.
We are tempted so that we can grow. The Book of Job is not a message about not blaming God for our misfortunes. It is a book about God being in control of our lives and we should never question why misfortune happens to us. It is a book that illustrates the principle that, "...God causes ALL THINGS to work together for good to those who love God..." (Rom 8:28). There isn't anything outside of God's control for our lives. In the end Job was far richer and wiser for his misfortunes as were his friends (wiser, that is).