Old Testament
There is much to learn about God in the Old Testament. It is basically a book about a covenant people and their relationship to a promised land. The Old Testament Scriptures were written over a period of 1000 years, from the time of Moses and the exodus from Egypt (1400s B.C.) to the final days of prophetic speaking to Israel through Malachi (400s B.C.).
Today they serve the Christian in a number of ways. They reveal the deity of God , the holiness of God, the reason for sin and death, the concept of covenant with God, the promises of blessings from God, and a host of other issues and topics; all revealed by God to man by the Holy Spirit's inspiration in selected individuals called prophets.
One thing to keep in mind when studying the Old Testament is that it points forward to the Messiah, Jesus Christ, and the fuller revelation of the "people of the covenant", meaning the Church.
Main Categories
Law
This first section covers the first five books of the Bible. Moses wrote them under inspiration of the Holy Spirit during the forty years that the Israelites wandered in the desert after being delivered from the harsh bondage of Egypt. Conservative scholarship places this event somewhere near 1450, while liberal scholarship around 1250 B.C.
God had created a nation overnight by delivering the Israelites from Egypt, and these writings are the foundational documents that (1) describe the heritage of Israelite origins, (2) depict the necessity of their need of God and God's desire to lead them, (3) define what kind of nation Israel was to be, and (4) establish protocol of a law-oriented covenant relationship between God and Israel.
History
This section of the Old Testament covers the next twelve Old Testament books of the Bible, from Judges through Esther. These writings deal with the history of the Israelites. It begins at the point where they entered the land of Canaan under the leadership of Joshua, the successor to Moses, forty years after being delivered from Egypt. It covers several hundred years in which judges ruled these covenant people, and a short period of a united kingdom under the kings Saul, David, and Solomon. It continues with the history and decline of a divided people--Israel, the northern kingdom, and Judah, the southern kingdom--and of the eventual demise of Israel (722 B.C.) and Judah (586 B.C.). Finally, this section closes with the return from captivity of a remnant of the descendants of those who had come from Judah, and of a specific miracle of preservation of these people--now called Jews--while Persia was in power. This entire era spans from a starting point between 1400 and 1250 B.C., and a closing point of somewhere in the 400s B.C. This period covers approximately an entire millennium
Poetry
The poetical books were, except for Job, poetical writings of the children of Israel (the "people of the covenant") expressing the great variety of emotions and desires and attitudes regarding their relationship to their God Jehovah. These books cover a vast array of topics from righteousness and reward to trust in God to praise and worship, and so on. Many believe that Job, in poetical style, was written before Israel was a nation, but relates directly to the matters of suffering and of judgment and righteousness--matters that pertain to the covenant people.
Major Prophets
This collection of five books has been named the Major Prophets, not because they are more important than the so-called Minor Prophets (the last group of books of the Old Testament), but because these works are much larger than the others. The size of the books seems to have been an influence in the Christian ordering of these books.
Remember too, that before binding of books as we know it, the books of the Bible were written on scrolls. The scroll of Isaiah, for example, could be picked up to be read without having to hold the scrolls of other books. The many scrolls of the Old Testament required the Jews to keep a list of the books written down, which basically followed the order in which books were written, or completed--for example Chronicles was the last book to be closed, and so is the last book of the Jewish Scriptures. Anyway, because of various factors, the Christian order of the Old Testament books differs somewhat from the original Hebrew order.
It should also be mentioned that Lamentations, which is only 5 chapters long, was written by Jeremiah. It is appropriately placed in this collection of the major prophets immediately after the book of Jeremiah.
Minor Prophets
This collection of twelve books has been named the Minor Prophets. As mentioned under the Major Prophets, these books are no less important than the Major Prophets. They are smaller in size. Also, it is important to remember that the Christian arrangement of books does NOT follow the chronological order in which the prophets ministered. It is interesting though that Malachi, which is placed last in the Christian order of books, was also the last prophet to minister to Israel during the 400s B.C.