The Old Testament takes up two-thirds of the Christian Bible.  The Hebrew Bible, the Tanakh, is divided into three major parts, the Torah, the Nevi’im, and the Ketuvim.  The Torah was known as the Law or instruction.  The works of the prophets was called Nevi’im.  Finally, the Writings were called Ketuvim.  New Testament writers used these three terms of the law, the prophets, and the writings when they referred to the Hebrew Scriptures, the only Bible that they knew.  Most of the final codification of the Hebrew Bible had taken place centuries before the time of Jesus Christ.  Thus, the Christians often referred to the law and the prophets when they were talking about the books of the Hebrew Bible.  These early Christians never referred to their own writings as the Bible.