A quote from J. G. Millar about our need to know the Old Testament in order to know the gospel. He mentions Deuteronomy in particular, but what he says applies to the whole Pentateuch (the first five books of the Bible):

Much of the theological framework needed to understand the significance of Jesus' coming, life and death was put in place by Moses in his writing, and perhaps above all in Deuteronomy. For it is here that the theology of blessing and curse which lies at the heart of Jesus' sin-bearing work is first articulated. It is here that the hopelessness of humanity trapped in sin, even when chosen by God, is exposed. It is here that the prospect of a divine intervention so radical that it changes people at the very core of their being first appears. (New Dictionary of Biblical Theology, pp. 164-165)