Theology is like an electric drill. The motor that runs theology is the Bible, the principium (the first principle). It underlies all the theological disciplines, just as the motor runs the drill. In considering a drill, nothing at all will work without the motor. In theology, we explore the meaning of Scriptures in exegesis. We explore what the church has said about the meaning of Scripture in church history (i.e., looking at God’s gifts of the Holy Spirit’s understanding and instruction given to teachers and preachers throughout the church’s history). We look at what the Scriptures say as a whole in systematic theology. We look at how the Scriptures apply to us in practical theology. We examine how we can remove obstacles (by God’s help) to an unbeliever’s coming to faith in God through the Bible in apologetics. What unites all the theological disciplines is the Bible. It is the motor of the drill.
To get the full use out of a drill, it is necessary to know how the parts work, and what all the switches and gears do. Knowing this about a drill is analogous to the exegetical enterprise. Or, to switch metaphors for a moment, exegesis looks at the individual trees in the forest.
Knowing something about the drill’s history can help us appreciate all that a modern drill can do. Hand drills, for instance, while having a charm of their own, and having the advantage of less noise, are also quite a bit (if you’ll pardon the pun) less efficient. This is similar to the function of church history. Studying church history helps us understand how and why we got where we are today. It helps us avoid the mistakes of the past, while also learning from the past so that the past can correct us where we are wrong (we need to make sure we avoid chronological snobbery here).
It is, of course, necessary to understand what a drill does as a whole if we are going to make any use of it. A drill makes holes in wood or some other substance. If we don’t understand its purpose, we might as well forget about using it as a tool, or we might be tempted to use it as a hammer. Understanding what a drill does in its entirety is similar to the project of systematic theology, which always has an eye on the other disciplines, learning from them, and informing them (not to mention guarding the other disciplines from error!).
This last named function of systematic theology needs defense, since most exegetes these days don’t particular like the idea of systematic theology having any role to play in exegesis (and some of them actively despise systematic theology). Systematic theology is a fence that guards our exegesis from error. If our systematic theology actually comes from the organic unfolding progressive nature of Scripture, then it will not be a straight-jacket, but rather the fence that keeps the children from going out into the dangerous road. Operating without a systematic theology is actually impossible, since the human mind cannot avoid synthesizing what it knows into a coherent whole. People who deny that they have a systematic theology actually very much have a systematic theology. It’s usually a very bad systematic theology, since the proponent of it tries to deny that it is even there.