The book of Job was written before God chose the Israelites, as His chosen people, during the time when there was no covenant which could possible save Job or for Job to have restored contact with God, which Adam lost (Gen 3:22).
Death reigned from Adam to Moses, even over those who had not sinned according to the likeness of the transgression of Adam (
Rom 5:14)
Therefore the author of Job wasn't a Jew. However,
salvation is of the Jews (
John 4:22, Rom 3:2).
The book of Job cannot be scripture and that cannot be refuted by opinion.