Reformed Theology Through the Lens of Biblical Theology

I'm (re-)reading Bruce Waltke's new Old Testament Theology, and came across an idea that, although not new to me, is explained here in such a way that has brought about fresh reflection.
The field of biblical theology seeks to read the Bible in such a way as to see the progression of God's work through history, sorting ideas thematically into organic categories that flow from the text rather than from philosophical categories (as is done in systematic theology). Biblical theology focusses on narrative and the historical development of themes.

A common endeavor in biblical theology is to state the center of Scripture, that is, the main tension that is resolved throughout the text. Although some biblical theologians believe there is not one central theme that can be named, many theologians—Waltke included—consider the center of the Bible to be the irruption of God's holy kingship into his creation. Says Waltke,

"...the center of the Old Testament, the message that accommodates all its themes, is that Israel's sublime God, whose attributes hold in tension his holiness and mercy, glorifies himself by establihsing his universal rule over his volitional creatures on earth through Jesus Christ and his covenant people."

[Bruce Waltke, An Old Testament Theology, 144]

Waltke says later that this theme implicitly spreads into the New Testament, where the kingship of God is mostly clearly demonstrated in Jesus Christ. Now, Waltke is admittedly reformed, but I think the pervasiveness of central themes similar to this one seen in Scripture gives a certain helping proof to reformed theology. I have often heard systematic proofs of reformed theology—often seen in the shape of TULIP. And there are many micro-level text proofs that show reformed theology's faithfulness to the biblical text. But in a new way, I recognize how reformed theology fits into the narrative of Scripture with a biblical theology centered in such a way as this. Through this lens, I want to briefly look at three ways Walke's statement of the central theme of Scripture informs and supports the core tennants reformed theology.

1. The Sovereignty of God

Waltke chooses the term "sublime" to briefly describe the glory of God, while his "universal rule" over the world shows the breadth of his sovereign rule. Further, it is God irrupting his kingdom onto the world, a reflection of his sovereignty in volition.

2. The Centrality of Christ

Because the Old Testament is about the Kingdom of God, it is implicitly about Jesus Christ, the one through whom God establishes his permanent kingdom on earth. As Christ takes the foreground even in the Old Testament, it becomes clear that the crucifiction of Christ was God's sovereign plan from the beginning—further heightening a sense of the sovereignty of God. Here see also Luke 24:27, where Jesus explains to his disciples how the whole of the Old Testament points to him.

3. The Doctrines of Grace

Waltke calls the entrance of God's sovereign kingship onto the scene of history as irruption rather than erruption. If a volcano errupts, an asteroid irrupts. This relates that God—and proper relationship with him—come not from within humanity but from God. He establishes his kingdom, and He calls his children into it. Irruption leaves no place for man-made religion. God breaks onto the scene in such a way that man must respond.

4. The Cultural Mandate

Waltke argues that "This in-breaking of God's rule involves battling against spiritual adversaries in heavenly places and political, social and religious powers on earth and destroying them in righteous judgment while saving his elect." God has chosen to show signs of the coming complete redemption of the earth by mercifully holding back evil in this age. To this end, his church is called to take the Gospel to the nations, but also to be involved in their own societies as a Gospel witness through word and deed. As Israel was indicted for injustice against the poor, so the church must seek to live justly in a corrupt culture.

5. The Doctrine of Scripture

Finally, seeing how the narrative of Scripture supports reformed theology further upholds the reformed emphasis on stressing the Bible's authority and innerrancy. As we see that God is working consistently to bring about his desired ends, we gain a greater trust in Scripture as well as a greater appreciation for all parts of the biblical narrative. They have all been given to us in order that we might know the creator and redeemer God who has established his kingdom through his only Son, Jesus Christ.