What is the difference between the Old and New Testament?

The Old Testament relates to the Hebrew people and their relationship with the Lord. Many of the books focus on laws that the Hebrews were given by people like Moses. Other books like Isaiah prophecy the coming of the Messiah. The New Testament is about Jesus Christ, who many believe to be the Messiah. The NT gives us the teachings of Jesus, the story of His life, death, and resurrection, and letters from people like Paul who had teachings for the followers of Jesus. Typically Christians see the NT as "fulfilling" the OT.

Both the Old and New Testaments are considered Holy and divine scriptures, yet not all of the Old has direct relevance for Christians, although even the Law of Moses has instructional significance as it points to the need for Jesus' perfect sacrifice. Much in the Old Testament is 'foundational truth' in that it establishes truths taught throughout scripture from the Old and carried over into the new. Examples of these would be the teaching on God as creator and sustainer of the universe, the origin of sin and the character of God.

As with any sacred writing, it is important to see to whom it applies and the ceremonial laws, as stated above, were given specifically to the Jewish people. And, although Jesus is both pre-figured and prophesied about in the Old, He becomes the central subject of the New.

Probably the most important difference to highlight is the change in man's relationship to God. In the Old it primarily involved external religious ceremonies. In the New it is an internal matter for the heart, beginning when a person is born again and being demonstrated in a righteous life, and witnessing to the person and work of Jesus Christ. Since Jesus has, in the New performed the once only sacrifice, no more 'work' is needed to earn salvation. Christians in the New Testament gladly follow in gratitude, not in order to earn anything, which can lead to either pride and self-righteousness or to uncertainty (have I done enough?) This is not to say that there is no joy in Old Testament, just that the basis for it has changed.

In addition to all this, while the idea that the Jewish faith was for all nations is most certainly evident in the Old Testament, it is very much more prominent in the New, particularly since the leaders of the Jewish religion rejected the Messiah and caused Him to be crucified.