The Bibles say, "A scripture is inspired by GOD..."
He inspired early Christians under apostolic authority to pen the actual parts.
"Early Christians" means members of the Church. You may, like Luther, doubt that the authority of the Bible came from the the Church. He obviously thought that HE was inspired to deny that authority. But, really, doesn't it means we have to choose between Luther's insight --if that is what it was--and the pronouncements of the Church of Rome? Luther appealed to Scripture and then declared himself more competant than Rome. Sort of like the Supreme Court's "finding" of a right of privacy in the Constitution.