Differences of emphasis and outlook within scripture. It was for many centuries CE held that the books of the Bible as bound together formed a coherent and consistent account of God's dealings with humanity. There was a unity between the two testaments and within each testament. The OT anticipated what was fulfilled in the NT: the OT was constructed round the central theme of the covenant between God and Israel, and anyone reading the OT in the 1st cent. would gain a fair idea of what Judaism was. The NT was held to offer an account of the salvation brought by Jesus, and the various terms used about him and his work in the gospels and the epistles were not contradictory; they could be interpreted by the standards duly prescribed by doctrinal formulations and were consistent with each other.
In the 18th and 19th cents. this basic unity was questioned. Parts of the OT were diagnosed as different sources with different theological presuppositions. In NT scholarship there was the suggestion that the fourth gospel gave a more advanced Christology than that of the synoptists who presented a human portrait of Jesus. Paul was sometimes identified as the real founder of Christianity, and within the NT itself a clash could be detected between Peter and Paul.
Although for a time in the 20th cent., during the predominance of Biblical Theology, there was a revival of support for the idea of the unity of the Bible, especially the unity of the NT, without surrendering the principles of historical criticism, that movement has spent its force, and it would now be widely agreed that there does exist much diversity of material and interpretation within the Bible. In the OT there is a large quantity of sheer narrative from Genesis to Esther, and within this some of it is rewritten from a new perspective by the books of Chronicles. Into the historical sections large sections devoted to Law are inserted. Then there are the psalms, a love song, Wisdom contributions, apocalyptic. It is not easy to assert the unity of such a diverse collection. In the NT there is a similar diversity of genre—history, parables, letters, prophecy, myth. There is also a variety of interpretations of Jesus—as Son of Man, as Logos, as Mediator—and of his work, of ransom, liberation, and healing, as the writers struggled to affirm their own experiences of belief in Jesus and life in the Christian community within changing social circumstances and against a cultural background which changed dramatically as the Church spread out into the Graeco‐Roman world and encountered many foes.
Yet despite the diversity there can be discovered a genuine unity within the Bible: belief in the One God which is explained most clearly in the sayings, and the life, death, and resurrection, of Jesus. He is the Lord whom gospels (John 21: 31) and epistles alike longed for their readers to accept and trust.