Theology develops over time—it seems obvious to me, but I have friends who disagree. Every theological doctrine has a history, beginning with the first person to think it and describe it, and then it is refined over centuries by many others. Hans Küng keenly compares the development of theology to the development of science in his excellent book, the Theology for the Third Millennium.
Küng says that Thomas S. Kuhn's The Structure of Scientific Revolutions applies to theological development. Science has developed through different models over time; the Ptolemaic model was replaced by the Copernican model, and then Newtonian model replaced it, and then the Einsteinian model replaced it, and so on. Each scientific model was made obsolete by later models that described the world more accurately. Küng says that theology has gone through the same revolution of models, such that the Augustinian model was replaced by the Thomistic model and then was replaced by the Reformation model, and so on. Each theological model improves upon the previous model and supplants the previous models.
The conclusion is that abandoning the Reformation model to return to a previous model such as the Augustinian or Thomistic models, would be tantamount to turning back from modern science such as the Einsteinian model to follow obsolete models such as the Ptometiac scientific model. Protestant theology is always returning to the bible, ad fontes, but never regressing entirely to outmoded theological models. We return to the Bible to advance our theological understanding of the Bible, but not to reject theological development, and nor to return to obsolete theological models of long ago.
Scientific and Theological Revolutions
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Hans Küng on Theological Revolutions:
In physics we can now distinguish between a Ptolemaic, a Copernican, a Newtonian, and an Einsteinian macromodel. Couldn't we make an analogous distinction in theology between a Greek-Alexandrian, a Latin-Augustinian, a Medieval-Thomistic, a Reformation, and one or several modern-critical interpretive models? [...]
Thus in physics, there would be macromodels for general scientific solutions (such as the Copernican, Newtonian, or Einsteinian model), mesomodels for the solution of medium-range problem areas (such as the wave theory of light, the dynamic theory of heat or Maxwell's electromagnetic theory), and the micromodels for scientific solutions of detailed problems (such as the discovery of X-rays).
The theological analogy for this would be macromodels for general solutions (the Alexandrian, the Augustinian, the Thomist, the Reformation model), mesomodels for the solution of intermediate problem areas (doctrine of creation, grace, the sacraments), and micromodels for solutions of detailed problems (doctrine of original sin, the hypostatic union in Christology). [...]
Even very well scrutinized "classical" theories like those of Newton or Thomas Aquinas have proved inadequate and in need of overhauling. There is no reason, then, to absolutize a method, a blueprint, or model. Instead we have every motive for an unrelenting new search, for permanent criticism and rational supervision: on the way through pluralism to even greater truth. 
[^1] Hans Küng. Theology for the Third Millennium: An Ecumenical View. New York: Doubleday, 1988. 134-35. Print.
Related: Augustine, Copernicus, Einstein, Hans Küng, Models, Newton, science, Theological Revolutions, theology, Theology for the Third Millennium, Thomas Aquinas, Thomas Kuhn