Most people in churches nowadays have never read through the Bible even once; the older Christian habit of reading it from start to finish as a devotional discipline has virtually vanished. So in describing the Bible we start from scratch, assuming no prior knowledge.
The Bible consists of 66 separate pieces of writing, composed over something like a millennium and a half. The last 27 of them were written in a single generation: they comprise four narratives about Jesus called Gospels, an account of Christianity’s earliest days called the Acts of the Apostles, 21 pastoral letters from teachers with authority, and a final admonition to churches from the Lord Jesus himself, given partly by dictation and partly by vision. All these books speak of human life being supernaturally renovated through, in, with, under, from and for the once crucified, now glorified Son of God, who fills each writer’s horizon, receives his worship, and determines his mind-set at every point.
Through the books runs the claim that this Jesus fulfills promises, patterns and premonitions of blessings to come that are embodied in the 29 pre-Christian books. These are of three main types: history books, telling how God called and sought to educate the Jewish people, Abraham’s family, to worship, serve and enjoy him, and to be ready to welcome Jesus Christ when he appeared; prophetic books, recording oracular sermons from God conveyed by human messengers expressing threats, hopes and calls to faithfulness; and wisdom books which in response to God’s revelation show how to praise, pray, live, love, and cope with whatever may happen.
Christians name these two collections the Old and New Testament respectively. Testament means covenant commitment, and the Christian idea, learned from Paul, from the writer to the Hebrews, and from Jesus himself, is that God’s covenant commitment to his own people has had two editions. The first edition extended from Abraham to Christ; it was marked throughout by temporary features and many limitations, like a non-permanent shanty built of wood on massive concrete foundations. The second edition extends from Christ’s first coming to his return, and is the grand full-scale edifice for which the foundations were originally laid.
The writer to the Hebrews, following Jeremiah’s prophecy, calls this second superstructure the new covenant, and explains that through Christ, who is truly its heart, it provides a better priesthood, sacrifice, place of worship, range of promises and hope for the future than were known under its predecessor. Christians see Christ as the true center of reference in both Testaments, the Old always looking and pointing forward to him and the New proclaiming his past coming, his present life and ministry in and from heaven, and his future destiny at his return, and they hold that this is the key to true biblical interpretation.
Christians have maintained this since Christianity began.--J. I. Packer, Taking God Seriously: Vital Things We Need to Know (Crossway, 2013), 21-22