What we call the ‘Old Testament’, consisting of the Law, the Prophets and the Writings is the foundational Scripture of Judaism. It is also the foundational Scripture of Christianity. As Jerusalem was sacked in 70 AD the Temple of the LORD was destroyed and the means and place vanished where Jews could have upheld the sacrifices prescribed in the Law, the five books of Moses. Out of this Rabbinic Judaism developed with the Mishnah (Oral Law) and the Talmud as a commentary and explanation of what was laid out in the OT.
Temple Judaism could not be practised in the absence of the Temple. True, this started before the Temple was destroyed by worship and Bible reading in local synagogues. The first Christians were Jews from the Galilee who, just like everyone else, met in these synagogues. However, there was never such a desperate need for revising theological principles as after 70 AD, something that was started at Yavne.
What was to become the New Testament is also a commentary and explanation of the OT in a similar way. The former out of necessity as the Temple was no more, the latter out of belief that the Messiah of the OT finally had come and fulfilled what He had promised. For these the Temple had played its role and was needed no more. Christ had been the ultimate sacrifice.
Let us label these two streaks of continued OT-religion as Israelite faith 1 (Rabbinic Judaism) and Israelite Faith 2 (Christianity). Terminology sometimes plays tricks with our minds. It is often perceived that present day rabbinic Judaism equals the faith of the OT, and that Christianity broke out as a sect, like many before and after. This is simply not the case. As seen by the above, OT-religion was forced to pick a route at the cross-roads in the first century – two main ways resulted, and let us call them as above to keep our mind free from bias: Israelite Faith 1 and Israelite Faith 2.
So, from a secular historical pint-of-view, these are the two ways of ‘dealing’ with the crisis of the destruction of the Temple. As has been indicated, circumstances speak favourably for Israelite Faith 2 since it chose route some decades before it would have been forced to, as opposed to Israelite Faith 1 which was left no other choice.
Maybe it was not so much a turn at the cross-roads that Israelite Faith 2 took, in the first half of the first century, but rather continued in the curve along the intended path, fulfilling OT-religion.
Maybe Israelite Faith 1 continued straight not taking heed of the curve, and ended up at the cross-roads in 70 AD.
Thus, viewing the coming into existence of the NT as the natural, God-intended continuation of the OT rather than some random off-shoot from OT orthodoxy (divinely inspired or not) restores the dignity rightly due to the OT.
And what is more, it makes sense of the NT.