The twenty-third book in the Bible, and first of the Prophetic Books, is the Book of Isaiah. There are seventeen Prophetic Books in all and they make up approximately one quarter of the Bible as a whole.
Isaiah is considered by many to have been the greatest of all the prophets. He served under four different kings of Judah, but became unpopular because of the harshness of his words.
The first 39 chapters in Isaiah tell us of holiness and God's justice (the main theme of the Old Testament as a whole) whilst the last 27 are about God's compassion (the theme of the New Testament). Coincidentally there are 39 books in the Old Testament and 27 in the New Testament.