Old Testament books were written up until 400 BC, beginning during the time of Moses. A thousand-year period is covered in the Old Testament outlining the creation of the Universe and Jewish people returning to Jerusalem under Nehemiah and Ezra. From AD 50 and AD 150 is when the New Testament is believed to have been written.
God’s works and power is chronicled in the Old Testament and the coming of the Messiah. Jesus is revealed as the Messiah in the New Testament. The New Testament covers His life and the teachings that are to be spread as gospel in the church.
The Old Testament looks to the future and focuses on prophecies. The New Testament focuses on the fulfilled prophecies and not the unfulfilled ones from the Old Testament. In the New Testament, there are over 300 fulfilled prophecies throughout the life of Jesus Christ.
The practice of worship differs between the two testaments. The Old Testament focuses on the temple, a central place of worship, or the tabernacle. There are plenty of details about festivals, offerings, and related practices. In the New Testament, Jesus Himself is the focus of worship and claims that he is the truth, the way, and the life. No one could directly reach the Father and had to go through Him (John 14:6).
Covenant is different between the testaments and the Old Testament focus on the Law of the Lord. The New Testament brings a new covenant and Jesus would come to fulfill the Law. People would no longer need to find atonement and fulfill the Law as Jesus offers eternal life and forgiveness for all who believe in Him.
Size is another difference. The Old Testament has thirty-nine of the Bible’s sixty-six books. Three-fourths of the entire Bible consists of the Old Testament. The New Testament has twenty-seven books, four Gospels, twenty-one letters, a book of Acts (history), and a book of Revelation (prophecy).
The Old Testament acts as a foundation for the New Testament. The Old Testament is nearly 75% of the Bible, it mainly points toward the Messiah who is fully revealed in the New Testament. Instead of a new message, the New Testament reinforces and reveals how Jesus fulfills the predictions and how His teaching, writings, miracles, and accounts of His early followers.