What is the difference between the Old and New Testaments?
The Old Testament was written primarily in Hebrew (a few short passages in Aramaic). Approximately one hundred years (or more) before the Christian Era the entire Old Testament was translated into the Greek language. Our English Bible is a translation from these original languages. The New Testament was written in Greek.
The Old Testament is the covenant God made with the people about their salvation before Christ came. The New Testament is the agreement God made with the people about their salvation after Christ came. The Old Testament is an account of a nation (the Jewish nation). The New Testament is the account of a man (the Son of man). The nation was founded and cultivated by God to in order to bring the Man into the world (Genesis 12:1-3). God Himself became a man (John 1:14; 14:9). His time spent on earth is the core event f all history. The Old Testament prepares us: for Christ's appearance and earthly mission. The New Testament describes it.
In the Old Testament we find the covenant of the law. In the New Testament we find the covenant of grace that came through Jesus Christ. One led into the other (Galatians 3:17-25).
The Old Testament commences what the New Testament completes. The Old gathers around Mt. Sinai, the New around Mt. Calvary. The Old is associated with Moses, the New with Christ (John 1:17).
The Old Testament begins with God (Genesis 1:1). From Adam to Abraham we have the history of the human race. From Adam to Abraham to Christ we have the history of the chosen race. The New Testament begins with Christ (Matthew 1:1). From Christ we have the history of the Church.