Many may already be familiar with the differences between these approaches to the study of theology. But for those who are unfamiliar, here is a succinct definition of each.
Systematic Theology: The systematizing of Bible doctrines into a logical coherence. For instance, what does the Bible say about the nature of God (theology proper)? What does the Bible say about sin (hamartiology)? What does the Bible say about salvation (soteriology)?
Covenant Theology: The study of the unfolding of redemptive history in its covenantal context — Adamic Covenant, Noahic Covenant, Abrahamic Covenant, Mosaic Covenant, Davidic Covenant, and the New Covenant. Covenant theology looks at the progressive nature of God’s revelation via the covenants, noting both the continuity and discontinuity between the covenants.
Biblical Theology: In a general sense, biblical theology is theology that is biblical. However, in a formal, academic sense, biblical theology is the study of the unfolding of redemptive history as revealed in its types, shadows, and symbols, and interpreted by the biblical authors themselves (i.e. the biblical authors interpreting or explaining earlier revelation).
As you’ll notice from these definitions, which I’m confident are widely held understandings of these approaches to the study of theology, only covenant theology and biblical theology are specifically and purposefully oriented around the history of redemption (i.e. God’s historical development of His plan of salvation, culminating in the Christ, Jesus). Systematic theology does not necessarily have this emphasis. But herein lies the downside of systematic theology. Don’t get me wrong, I think systematic theology is important, even necessary. I actually think we see a glimpse of systematic theology in Paul’s words to Timothy when he instructs Timothy to “Retain the standard of sound words which you have heard from me, in the faith and love which are in Christ Jesus” (2 Tim. 1:13 NASB ’95, emphasis added). The ESV says “the pattern of the sound words”. In fact, all three of these theological studies are important and necessary for the Church. They ought to be studied together. The problem is that systematic theology has largely been the primary approach to theology, and it is often done in complete isolation from the other two.
The Scriptures themselves, however, set up for us the necessity of studying systematic theology in the context of covenant theology and biblical theology. As an example, we find important teaching on sin that informs our systematic theology (hamartiology) in Genesis 6:5, 11-12:
Then the LORD saw that the wickedness of man was great on the earth, and that every intent of the thoughts of his heart was only evil continually…. Now the earth was corrupt in the sight of God, and the earth was filled with violence. God looked on the earth, and behold, it was corrupt; for all flesh had corrupted their way upon the earth.NASB ’95
There’s plenty there to chew on in a systematic study of man and sin. But we have to remember, this is given to us in the context of the Adamic Covenant (previous to this text) and the Noahic Covenant (following this text). How are we to understand this text in the context of mankind’s covenant relationship to Adam? How are we to understand this text in the context of the impending global flood and the promise given to Noah and all of creation in the covenant God makes with him? I won’t go into answering these questions here, as that is beyond the scope of this post. But I hope you get my point.
More examples can be supplied. One striking example is found in Romans 5:12-21. Here Paul is teaching on the law, sin, and salvation. However, he is not merely systematizing these doctrines, but explaining them in the context of covenant and biblical theology. In short, he explains our sin in relation to Adam’s covenant headship over all humanity, and then shows that we must be united to a new head, Jesus Christ, by grace through faith. He even says that Adam “is a type of [Christ]” (v. 14). In other words, Paul is explaining sin and salvation in the redemptive historical context of the Covenant of Works with Adam and the Covenant of Grace with Christ, showing Adam to be a type — a prefiguring — of Christ.
Covenant theology and biblical theology serve as the interpretive grid for our systematic theology. It is therefore vital that we study systematic theology in the context of both covenant theology and biblical theology.