Many people try to read the Bible like two novels, expecting a chronological story.
This is not how it was written or compiled. The New Testament is about our new covenant of salvation through Jesus Christ. In the Old Testament, people were forgiven and received salvation through rigorous attention to the Law and through sacrifice. Now, we receive salvation through faith in Jesus Christ, who died once for all of us. The New Testament tells us how Christ can have the authority to pay the penalty for our sin and how the new covenant works.