From author David Clines, Deconstructing the Book of Job
According to the Satan, God must be thinking that Job does fear him gratuitously, that the piety of Job therefore is unmotivated and is the origin of his prosperity. The Satan’s own suspicion is that it is the other way around, and that it is Job’s prosperity that is the origin of his piety, that it is only in order to become prosperous or remain prosperous that Job is so exceptionally pious. When the point is put to him, God has to admit that he does not know the difference; he had been assuming all along, as do most humans, that the principle of retribution runs from the deed to the result, and not from the result to the motivation. God therefore has to allow an experiment to be carried out on Job to discover whether the dogma of retribution, to which he has been giving his assent, is true.