It is now not only admitted by intelligent and honest theologians that Moses was not the author of the Pentateuch, but they all admit that no one knows who the authors were, or who wrote any one of these books, or a chapter or a line. We know that the books were not written in the same generation; that they were not all written by one person; that they are filled with mistakes and contradictions. It is also admitted that Joshua did not write the book that bears his name, because it refers to events that did not happen until long after his death.
No one knows, or pretends to know, the author of Judges; all we know is that it was written centuries after all the judges had ceased to exist. No one knows the author of Ruth, nor of First and Second Samuel; all we know is that Samuel did not write the books that bear his name. In the 25th chapter of First Samuel is an account of the raising of Samuel by the Witch of Endor.
No one knows the author of First and Second Kings or First and Second Chronicles; all we know is that these books are of no value.
We know that the Psalms were not written by David. In the Psalms the Captivity is spoken of, and that did not happen until about five hundred years after David slept with his fathers.
We know that Solomon did not write the Proverbs or the Song; that Isaiah was not the author of the book that bears his name; that no one knows the author of Job, Ecclesiastes, or Esther, or of any book in the Old Testament, with the exception of Ezra.
We know that God is not mentioned or in any way referred to in the book of Esther. We know, too, that the book is cruel, absurd and impossible.
God is not mentioned in the Song of Solomon, the best book in the Old Testament.
And we know that Ecclesiastes was written by an unbeliever.
We know, too, that the Jews themselves had not decided as to what books were inspired — were authentic — until the second century after Christ.
We know that the idea of inspiration was of slow growth, and that the inspiration was determined by those who had certain ends to accomplish.
Robert G. Ingersoll, 1894