The Old Testament ends with the book of Malachi. This final book is traditionally considered the last of the prophetic writings and serves as a conclusion to the messages of the prophets sent to the people of Israel.
Malachi addresses several key themes, including the faithfulness of God, the importance of maintaining a proper relationship with Him, and the coming judgment. It also speaks of the coming messenger who will prepare the way for the Lord, which Christians interpret as a reference to John the Baptist and ultimately to Jesus Christ.
In summary, the Old Testament closes with Malachi, bringing the narrative of the Hebrew Scriptures to a powerful conclusion and setting the stage for the New Testament.