The theological truth of this is that when we read our Bibles from Old through the New Testaments, we are reading the story of one God, one Savior, one means of salvation through faith, and therefore one people despite their chronological, geographical, and racial differences.
For many of us who have discovered the Reformed expression of the Christian faith after years in other traditions, “covenant theology” was one of the most eye-opening facets of it. It was more than just another part of theology, though. It was like getting a new pair of glasses. The old way we saw the Bible with Israel in the Old Testament and the Church in the New Testament was like an old, worn out pair of glasses with scratches and lots of scuff marks. This new pair allowed us to see clearly that our one Bible has two complementary testaments.
Of course many will say that this is a theological grid that we’ve imposed upon the Bible. We can take heart, though, that our ancient forefathers such as Justin Martyr and theEpistle of Barnabus viewed the scriptural understanding of its own diversity within unity. During the Reformation men such as Heinrich Bullinger and John Calvin read the Bible in this way to explain how Old Testament saints were saved and why we baptize children, speaking of the one covenant of grace despite varied times and places in which that covenant was expressed.
The Westminster Larger Catechism follows this ancient Christian and classic Protestant way of reading the Bible, of seeing God’s one story with its various acts. What it says is that we have One Bible, Two Testaments.
First, when you read your Bible, recognize its unity. There is one covenant of grace, that is, one plan and story of God the Creator becoming the Redeemer of sinful humanity.
One example of this is in Romans 11. In seeking to answer the conundrum that because most Jews rejected Jesus this meant God’s promises failed, Paul gives two images to describe God’s ancient promises to the Israelites and the fulfillment of them to the Gentiles: “If the dough offered as firstfruits is holy, so is the whole lump, and if the root is holy, so are the branches” (Rom. 11:16). These images both are meant to impress upon us the unity of God’s work from ancient times through the present.
The first image is that of bread. If the firstfruits of the dough is holy, then the entire batch of bread is holy. There is one batch of dough. Like a baker, God cuts off the first portion to make a loaf; if it is acceptable, then the entire batch will be acceptable. This is his way of saying that God has one plan of salvation. Those whom he called to be his holy people, beginning with Abram, and all those to follow partake of the same calling, the same salvation.