We have to distinguish a difference between doing theology and presupposing theology. It can be easy to replace one for the other and most people do a lot more presupposing theology than they actually do theology. We have a lot of imbedded concepts that we take for granted. Much of what we believe as biblical truth is actually theology that’s been passed on through generations and isn’t found specifically in scripture. Because we’ve been reared up in this western culture we sometimes are more influenced by western philosophy than we actually are by the scriptures.
When we say things like “Jesus loves me” or “God knows…” or “…this I know for the bible tells me so” we are usually presupposing such theology. Most of us haven’t truly stopped to ask why or how, especially if we’ve been raised in Christian homes. How do you know Jesus loves you? Just what exactly does God know? Just because the bible tells you so does that make it true? Why is the Bible so special anyway? We don’t usually stop to ask these questions. We don’t always take responsibility for what we believe. We arrive at a conclusion before, sometimes long before we ever ask why and there are probably many concepts that orchestrate your faith that you still haven’t thought trough. This is presupposing theology.
To actually do theology involves actually asking the question. It’s working toward the conclusion. To do theology is to never take lightly any statement about God or about how He deals with His people. The single largest differentiating factor between doing and presupposing is the question why. It’s our responsibility to ask why. The conclusions may not change completely but your life will and that is what really matters. Christianity is not a compilation of conclusions it is a journey of faith. Questions are essential to faith because faith is assurance of things unseen, unknown, undiscovered.
Many have separated theology into two main categories: “practical” and “systematic” theology. There should not be such a sharp distinction between these categories in fact they must overlap for either to function. For theology to be systematic and not practical would be missing the point on theology in general. The purpose of theology is ultimately practical, having to do with the life of the Christian. In the words of theologian Stanley J. Grenz; “Theological commitment must be applied to life – to the theologian’s own Christian walk and to the life of the Church – in order that faith can issue forth in discipleship.” Discipleship is the theologians goal; both for himself as an individual and for the church.
For theology to be practical without being thoroughly thought trough is also irresponsible. The task of theology is the expression of Christian faith. We mustn’t skip the expression and move right on into the application for in doing so we put ourselves at risk of applying a false and harmful orthodoxy. We cannot bypass the means to get to the ends. We walk responsibly considering what it is we are putting our faith in. There is therefore no such thing as a practical theologian or a systematic theologian for every theologian must be systematic in order to be practical.
 Stanley J. Grenz, Theology for The Community of God (Grand Rapids: Wm. B. Eerdmans Publishing Co., 2000) 25.