The Old Testament is divided into five sections: the Pentateuch (Genesis through Deuteronomy), the historical books (Joshua through Esther), the poetic books (Job through Song of Solomon), the Major Prophets (Isaiah through Daniel), and the Minor Prophets (Hosea through Malachi). The Old Testament was written from approximately 1400 B.C. to approximately 400 B.C. The Old Testament was written primarily in Hebrew, with a few small sections written in Aramaic (essentially a variation of Hebrew).
The Old Testament deals primarily with the relationship between God and the nation of Israel. The Pentateuch deals with the creation of Israel and God establishing a covenant relationship with Israel. The historical books record Israel’s history, its victories and successes along with its defeats and failures. The poetic books give us a more intimate look at God’s relationship with Israel and His passion for Israel to worship and obey Him. The prophetic books are God’s call to Israel to repent from its idolatry and unfaithfulness and to return to a relationship of obedience and spiritual fidelity.
The word "old" tends to give the idea of "outdated" or "not-relevant." That could not be further from the truth.
The Bible more completely is divided into two sections: the Old Testament and the New Testament. The word testament means “covenant.” A covenant is an agreement between two parties, with terms set by the initiating party that are fully accepted by the one entering the agreement. Testament and covenant are used interchangeably throughout the Bible. We call the first section of the Bible the “Old Testament” because it contains the record of God’s interactions with man from creation to the years before the coming of Jesus. The 39 books written before Jesus’ coming, detail life under the old covenant, thereby giving the name for that section. After Jesus came, He instituted a new covenant, which did away with the old sacrificial system (Hebrews 9:15). The 27 books penned after Jesus’ ascension into heaven detail God’s new covenant with man. So the names Old Testament and New Testament are accurate descriptions of what the books contain.
Within the Old Testament are separate covenants that God initiated with mankind through the centuries. These covenants, or testaments, were agreements between God and specific people whom God would use to further His purposes upon the earth. There are several such covenants in the Old Testament, such as the ones with Noah (Genesis 9:8–17), with Abraham (Genesis 12:1–3), and with Moses (Exodus 19–24). Each covenant was sealed with a specific sign or ceremony, often involving the shedding of blood (Genesis 15).
The Old Testament covenants detail God’s provision for the forgiveness of sin (Numbers 15:25–27; Leviticus 4:31). These provisions were complicated and costly, requiring the intervention of priests and the bloodshed of perfect lambs, bulls, and goats (Hebrews 9:22). God was painting a picture so that humanity could understand the high cost of sin. Until we see how offensive our sin is, we don’t appreciate what it costs God to forgive it.
When Jesus came to earth, He instituted a new covenant for everyone who believes in Him (John 3:16–18). His own blood would be the seal of this covenant (Luke 22:20). Christ fulfilled the Law to perfection so that, when He went to the cross, He is the perfect and final sacrifice for the sins of the world (Matthew 5:17; Hebrews 9:14; 10:14). When Jesus died, the temple veil was ripped from top to bottom, signifying that mankind was now invited into the Holy of Holies through Jesus, the Door (John 10:9; Hebrews 10:20).
Even though the Old Testament books come first in our Bibles, the better name for this section of 39 books is Old Testament rather than First Testament. They detail the old law, the old way of gaining forgiveness, and the old way of receiving grace from God. The word old can mean “outdated and replaced,” which describes the old system that focused primarily upon the Jewish nation. The new system replaced the old with the sacrifice of Jesus. The new covenant offers salvation to “everyone who believes: first to the Jew, then to the Gentile” (Romans 1:16). We can fully appreciate New Testament when we understand the Old.