David Powlison comments on the relationship between the Christian life, systematic theology, biblical theology, and practical theology, in his class The Dynamics of Biblical Change:
“A relevant understanding of Scripture must match a deeply rich and textured understanding of people and the world in which people live. If you only know the Bible, and you only know your faith in its theological, historical, and biblical aspects, there is a sense in which you will only ever be an academic. You will only know theoretical knowledge. On the other hand, if you only know people, you will only know tens of thousands of facts, and you may become a poet or novelist or film-maker, but you will not have a living and life-giving wisdom. It is only when you have both that you will be a wise person, a wise pastor, a wise counselor and friend. Just knowing Scripture, and not knowing people, or just knowing people and not knowing Scripture will fail to make a connection between the “big T” truth of God’s word and the “little t” truth of life-lived.
Systematic theology teaches you to understand your faith. It gives you basic categories. It starts with things like the apostles creed. But they are essential and basic categories. What is the Father like? What is God like? Who is Jesus Christ? What did he do? Who is the Holy Spirit? What is man? What is human nature? What is the fourfold state of human nature – created, fallen, redeemed, finally connected? What are Christian relationships? There is this dense web of interconnected doctrine that is multifaceted in its beauty.
Biblical theology, like systematics, gives you these beautiful narrative categories. It’s the way God works. It’s the way Scripture unfolds. We’re given these very broad categories like the creation of all things. What is redemption, and why does redemption have this structure of promise and fulfillment?
As you grow in categories, theology gets richer and richer. Practical theology is a discipline. Practical theology seeks to teach you how redemption unfolds individually and corporately. In the same way that you have these very orienting categories in systematics, in practical theology, you have these basic categories of how people live and change.”