Before we can understand why systematic theology is essential, we must first understand what it is. There’s no single definition of systematic theology, but at its heart it’s the discipline captured by the phrase “faith seeking understanding.”
Systematic theology builds on the results of biblical theology. Biblical theology is the exegetical discipline that seeks to grasp the entirety of Scripture as the unfolding of God’s plan from Genesis to Revelation. Starting with Scripture as God’s Word written through human authors—our final authority (sola scriptura) for what we think about God, ourselves, and the world—biblical theology seeks to “put together” the entire canon in a way that’s true to God’s intent.
Systematic theology then applies the truths gained in biblical theology to every aspect of our lives. It leads to doctrinal formulation—what we ought to believe and how we ought to live—warranted by the canon and done in light of historical theology.
In this way, systematic theology constructs a well-thought-out worldview that enables the church rightly “to think God’s thoughts after him” and to set biblical truth over against its worldview competitors. The goal of systematic theology is “to bring every thought captive to Christ” (2 Cor. 10:1–5) for our good, for the life and health of the church, and most significantly for God’s glory.
Here are four critical things we can’t do without systematic theology.
1. KNOW GOD
Systematic theology is necessary to know God rightly as the triune Creator-covenant God (and nothing is more important than this!). It’s true that God has revealed himself in creation, and we know him from what he has made (see Ps. 19:1–6; Rom. 1:18–32). But God didn’t create us to know him merely from our study of creation; he spoke to us in words through the prophets and ultimately through our Lord Jesus and his inspired words through his apostles (John 1:1–18; 2 Tim. 3:16–17; Heb. 1:1–2; 2 Pet. 1:20–21).
But to know God truly we must know not only all of Scripture but also how to “put together” (by theological formulation) all that Scripture teaches.
For example, think of God as triune. The doctrine of the Trinity is true to Scripture, but it’s also the result of careful reflection on all that Scripture teaches about God’s oneness as God and threeness as Father, Son, and Spirit, plus much more. The Trinity isn’t found in one verse or chapter but in the entirety of Scripture, and unless systematic theology is done correctly, we won’t know God rightly.
Or think of the divine sovereignty-human freedom relationship. Careful theological reflection on the entire canon is necessary in order to get this truth right, which matters greatly in our daily lives.
Apart from theology, our grasp of who God is and even our trust of him in this fallen world will be less than what it should be.
2. KNOW OURSELVES
Systematic theology is also necessary to know who we are as God’s image-bearers and what God requires of his people. Theology tells us that the Bible’s story is unpacked with the categories of creation, fall, redemption, and new creation. As we try to understand who we are, we must carefully ask what God created us to be, what has happened to us in our sin, and what Christ has achieved in our redemption and ultimate glorification. If we don’t view ourselves this way, we’ll fail to grasp a truly Christian worldview.
In addition, theology is necessary to make sense of what God requires us of today. We know we can’t randomly apply Scripture to our lives without interpreting it in light of Christ’s coming.
But how do we discern what applies to us and what doesn’t? Answer: theological thinking about the entire biblical canon. Given that God has revealed his plan over time to us, we must wrestle with how the parts fit with the whole, and how the whole applies to us today.
Systematic theology, built on biblical theology, is required to do this; and apart from a well-done theology, we’ll often make mistakes (like the one the Judaizers in Galatia made because they didn’t attend to Scripture rightly).
Systematic theology affects our lives by helping us make correct application of Scripture to our lives as God’s new covenant people.
3. BE THE CHURCH
Systematic theology is also necessary to fulfill our calling as the church. What’s our calling? It’s to know God rightly and to live as redeemed image-bearers—which is tied to theologizing. In addition, our calling is to proclaim the gospel to the nations (Matt. 28:18–20). But what is involved in this proclamation?
First, it’s to proclaim a specific view of who Christ is as Lord—which depends on systematic theology. After all, who is Jesus? In the teaching of Scripture and the church, he’s God the Son incarnate. But what does this mean? How do we make sense of the fact that Jesus is the Son from eternity who is fully God and fully man? Systematic theology is necessary to proclaim who Jesus is as the only true Lord.
Second, it’s to proclaim his atoning work. What did his cross achieve? What does it mean that Jesus died “for our sins” (1 Cor. 15:1–3)? In church history people haven’t always agreed on this point, so theology is necessary to proclaim Christ rightly to the nations.
More illustrations could be given, but the point is this: to proclaim the gospel and fulfill our calling as the church requires systematic theology.
4. DEFEND THE FAITH
Finally, systematic theology is necessary to defend the faith once delivered to the saints (Jude 3). But to defend the faith assumes a certain content to the faith—which is tied to systematic theology. In addition, it assumes we know the truth as an entire worldview over against the errors of the world. Apologetics, or the “defense of the faith,” is bound up with systematic theology and, apart from it, we won’t fulfill our calling to proclaim Christ and defend the truth of gospel grace (Titus 1:9; 1 Pet. 3:15–16).
Systematic theology isn’t optional for Christians. Everyone has a systematic theology, whether they acknowledge it or not, and everyone’s theology practically affects their lives for good or ill.
So the question isn’t whether to take theology seriously but whether our theology will grow to be more true to Scripture, thus enabling us to live faithfully before our triune God and to proclaim the truth of the gospel before a watching world.