By inspiration we mean that this book is not written by human authors but by God himself. This does not mean that the Bible dropped out of heaven one day. Human beings, most of whose names we know, wrote the words in this book. But these authors were inspired by the Holy Spirit. Even this idea of the inspiration of scripture is not something humans thought up.
Every decision made in life is based on some authority.
It you want to know about the law you go to a lawyer who knows the laws of the land. If you are sick, you go to a physician who knows medicine and has access of the latest medicine knowledge. If we want answers about God, faith and ethics, you go to the Bible. Then you start relying on a man's interpretation of the Bible rather than the Bible itself. That got to such a point in the Roman Catholic Church that the Bible was on the prohibited list right up until the middle of this century.