Systematic theology is any study that answers the question, “What does the whole Bible teach us today?” about any given topic.This may seem innocuous enough to some readers, but it put me in mind of certain older philosophies of science. Specifically, the view that the task of the scientist is merely to gather and summarize observations in order to establish various more or less simple ‘laws of nature’. One suspects this was the view of science to which Ernest Rutherford was objecting when he said ‘All science is either physics or stamp collecting.’
This definition indicates that systematic theology involves collecting and understanding all the relevant passages in the Bible on various topics and then summarizing their teachings clearly so that we know what to believe about each topic.
Like Rutherford, I think this ‘stamp collecting’ approach to science is inadequate. Science should be about more than merely summarizing observations. Rather it involves the proposing and testing of theories – proposing models to explain how the world works – e.g. light behaves like a wave. Further, most physicists regard their theories as models of what is really going on rather than merely as heuristic devices for making predictions about the world. What is really of interest is not the prediction of particular experimental outcomes but the model itself as an understanding of reality.
Nor is ‘stamp collecting’ an adequate approach to theology. Theology is more than a mere summary of what the Bible says. Faith seeks understanding: drawing out the implications of what the Bible says to get a better understanding of God and God's relation with the world. For example, there is no way you can arrive at the full orthodox doctrine of the Trinity if you strictly limit yourself to summarizing what the Bible says on the topic. And yet the doctrine of the Trinity is the very foundation of orthodox Christian belief.
How then should we approach theology? My own preference is for the answer given by Robert Jenson in the introduction to his little book Story and Promise: A Brief Theology of the Gospel about Jesus (Fortress Press, 1973):
Theology is the persistent asking and disciplined answering of the question: Given that the Christian community has in the past said and done such-and-such, what should it do now? The question may be divided: (1) What has the Christian community in fact said and done? and, (2) What should it say and do in the future? The first sub-question, pursued within the context of the whole question, gives historical theology. The second sub-question, likewise only when pursued within the context of the whole question, gives systematic theology. (p. vii)