Biblical theology is a branch of Christian theology that most often deals with the historical progression of people's knowledge about God as described in the Bible. The study of biblical theology traces the history of interactions between God and humans. Its earliest proponents, including Geerhardus Vos (1862-1949), viewed biblical theology as contrasting some of the rationalistic trends in systematic theology, since biblical theologians usually believe in the supernatural to a greater extent than other theologians.
Despite some historical tensions, systematic theology and biblical theology generally have a complementary relationship with slightly different aims. Whereas systematic theology attempts to classify or describe what is known or proposed about God according to logical formations, biblical theology seeks to trace the history of how such knowledge of God was revealed in the Bible. In other words, systematic theology tends to have a topical approach, whereas biblical theology more often takes a historical approach to knowledge or propositions about God.
Vos and most other biblical theologians argue that the Bible contains a set of progressive revelations about God's nature. The Old Testament introduces the character of God and the history of God's dealings with humans, particularly the Israelites. God's redemption of His people through Jesus Christ is the subject of the New Testament. These two major segments of Scripture tell the story of redemptive history. According to this view, everything in the Old Testament should be viewed as foreshadowing or pointing toward Jesus, while the New Testament can only be properly understood as the continuation of redemption that was begun in the Old Testament.
In order to hold to this particular view, scholars generally must presuppose certain assumptions about the Bible. Whereas many other biblical scholars or systematic theologians see the Bible as simply a religious text and may not believe in God at all, most biblical theologians hold that the Bible is the authoritative word of God. Much of a biblical theologian's view of the Old Testament, for instance, is based on the assumption that the history of the Israelites is purposefully leading toward a future event — the coming of Christ, which could only happen supernaturally.
While the discussion of redemptive history is the most common type of biblical theology, the term is also sometimes used to describe other types of theological inquiry. One type has sometimes been called phenomenological, meaning that it seeks to describe the beliefs of certain people at certain times — as in the beliefs of the Israelites during the exile to Babylon. Others might view exegetical theology — the attempt to use relevant information to determine the exact meaning of a biblical author's words — as a branch of biblical theology. Those practicing this type of theology would not necessarily hold to the same presuppositions about God and Scripture that others probably would.