In the Scriptures, through many human authors in many circumstances, the one God speaks (Heb 1:1), and the unity in this diversity leads us to God’s final Word: Jesus Christ. Biblical theology is the attempt to relate the diversity and the unity alongside the likewise important disciplines of exegesis and systematic theology, all with the ultimate goal of beholding God. Though the Bible has so many authors, it was written by God. God picked the authors of the Bible, so they were prepared to speak for Him. God’s Spirit inspired them to say exactly what He wanted to say to His people!
What is biblical theology? It’s not just theology that is ‘biblical.’ All good theology sits under the authority of Scripture and seeks God’s revelation of Himself in it, but there are several important types of theological study. Biblical theology seeks to understand the unity and diversity of Scripture’s expressions by comparing the Bible’s parts to its other parts in light of the whole canon. Those parts might include a phrase, metaphor, theme, pattern, book, author, genre, section, or even testament (Old or New). When one of these parts is compared to another of these parts or to the whole canon, biblical theology is happening.
There is obvious diversity of expression and emphasis in Scripture, because God spoke through many human authors in many genres on many occasions (Heb 1:1). There is nevertheless unity in Scripture, because it is the one triune God who breathes out all Scripture (2 Tim 3:16), from whom and through whom and to whom are all things (Rom 11:36). Sound biblical theology is biblical not only because it takes God’s Word as its authority and source but because it is occupied with the literary particulars of Scripture, its diverse expressions, its canonical structure (for example, there is both an Old Testament and a New Testament), and the way later books refer to earlier books. It is also theological because it takes all these books as God’s one Book revealing God’s own essential nature through His economy, that is, His interactions with His creation, chiefly through the work of the incarnate Son. Indeed, “All Scripture is a testimony to Christ, who is Himself the focus of divine revelation” (Luke 24:27).
Biblical theology benefits our exegesis and our systematic theology. It can help us to understand the richness of any given part or passage of Scripture as we study, teach, or preach it. It can also help us see how Scripture’s structure and story support or correct our systematic theology. Biblical theology also benefits from these sister disciplines. For example, the particular grammatical construction of an NT quote of the OT can help us discern whether the NT author is trying to draw out a particular implication of the OT text or perhaps re-apply it to a new context in a new way.