Why do Theology, much less, Systematic Theology? Differing views on Theology abound in Christian thought. Isn't Theology just for scholars? Isn't this discipline reserved for seminary students and people who just like to argue. No doubt there are those who seek to make Theology a single faceted discipline and treat it simply as an academic issue. This plainly is not the purpose of Theology. The discipline of the study of God is meant to lead one into a deeper faith and knowledge of God. Not just with the mind but with all of one's being. Some might say "I don't do Theology, I just need the Bible." Maybe you have heard this slogan: "No creed but Christ". R.C. Sproul once pointed out, "Everyone is a theologian, the only question is, are you a good one?" Everyone has a certain Theology that they hold to, even non-Christians (Romans 1:18), but if anyone is a theologian (maybe not professionally) it's the Christian. He holds to certain beliefs about God and he acts on those beliefs. This is why we must intentionally seek to do Systematic Theology, because invariably what we believe about God will effect the way we live our lives. Holding doctrines in the air as if they do not have any relation to one another should not be the intention of the Christian. Such a mindset leads to inconsistencies that ultimately do not glorify God. So if the Christian is obligated to do Systematic Theology, then how is one to go about this task?
Of course older works from Berkhof and Hodge and even newer ones like Grudem and Horton will aid in the Christian's study, but first and foremost Theology is derived from the exegesis of the text of Scripture. If it is derived from elsewhere your footing is shaky at best. There is only one infallible rule God has given to His church and that is Scripture, even general revelation (creation) must be filtered through the lens of special revelation (Scripture). There also must be the highest view of Scripture, that is we must believe that the Scriptures are God breathed (2 Timothy 3:16). If we don't believe that, then Scripture is not objective revelation from God. Hence the Bible becomes a relativistic mish-mash of varying interpretations, with one interpretation not being better than another. In a recent interview with a mega church Pastor, Piers Morgan said, "...shouldn't the Scripture be dragged kicking and screaming into the modern age?" Such are the words of one with a low view of God's Word. Since Scripture is God's objective revelation to mankind it is not subject to the ever changing whims of modern culture. The Bible has revealed that God is immutable (Psalm 102:25-27) and not the author of confusion (1 Cor. 14:33); hence the need for Systematic Theology.
The Doctrines of the Christian faith are not to be held as separate compartments. Reformed theologian B.B. Warfield remarked, "We do not possess the separate truths of religion in the abstract; we possess them only in their relations and we do not properly know any one of them nor can it have it's full effect on our life...except as we know it in it's relation to other truths, that is, as systematized." If we do not see how a particular doctrine affects another then we are bound to misconstrue them. For instance, can the Reformed doctrine of substitutionary atonement be held at the same time as the Arminian doctrine of the universal atonement? Can God's absolute exhaustive foreknowledge be held at the same time as a doctrine of autonomous free will? If we are to be consistent in our Theology these are the types of questions that need to be dealt with. As Christians we believe that God is completely consistent and that likewise applies to the doctrines He has revealed in Scripture.
Systematic Theology not only leads the Christian to consistency, it also helps with his worship of God. By knowing how the doctrines revealed in Scripture cohere with one another, the Christian is brought to a deeper and more profound view of God. As pilgrims on our way to glory, we will not have perfect Theology. However true this might be, the Christian is still obligated to bring the doctrines of the faith together using the only infallible rule possessed by the Christian, Scripture. The Christian worldview is consistent and we should not present inconsistency to the world by letting our doctrine flounder.