Why there is different book arrangement between Christian Old Testament and Jewish Tanakh?
The Jewish Tanakh is organized according to genres. The Torah, or Law, is first (also known as the Pentateuch). Then the Nebicim, or Prophets. This begins with the former prophets (Joshua, Judges, Samuel-Kings) and is followed by the latter prophets (Isaiah, Jeremiah, Ezekiel, and the 12 minor prophets). Finally the Ketubim, or writings (Psalms, Job, Proverbs, Ruth, Song of Songs, Ecclesiastes, Lamentation, Esther, Daniel, Ezra-Nehemiah, Chronicles) A few points of interest: the last chapter of Proverbs, Ruth, and Song of Songs all discuss women (particularly the virtuous woman) and are arranged in that order. Ruth, Song of Songs, Ecclesiastes, Lamentation, and Esther are called the Megillot – each book was associated with a particular Jewish festival. Several books in the Jewish Tanakh were divided into more books in the Greek-English Old Testament because of the number of scrolls it was written on. For instance, 1 Samuel through 2 Kings was actually one book, but a book that large co