The Necessity of Dogmatic Prolegomena
Since the 17th century, Barth has noticed prolegomena getting larger and larger in dogmatics, and much to his disdain. These prolegomena deal with apologetics or polemics against the modern skepticism which encroaches upon the dogmatic task. As Emil Brunner put it: "The problem to-day is not the nature of God but His existence, not what is revealed but whether there is such a thing as revelation, not rationalistic corruption at individual points but the questioning of the miracle of revelation as such. It is the problem of the sign and norm of all Christian theology, of the concept of revelation and not its contents. In short, it is the problem of reason and revelation."
In Barth's view, apologetics or polemics (or "eristics," as Brunner likes to call it)
suffer from the disadvantage that they might become a distraction from the true dogmatic task. Furthermore, although it aims at "relevance," it can easily miss this altogether by taking itself too seriously. Theology which does its own job will be the best apologetics. If prolegomena are needed, the necessity arises, not in relation to unbelief, but in relation to error in the church itself. Alongside truth in the church there is also heresy. Dogmatics, having a primary concern for the content of the Church's confession and proclamation, must obviously learn how to distinguish between heresy and truth. Barth finds in the modern period two erroneous movements: Roman Catholicism on the one side, and Liberal Protestantism on the other. The presence of these two movements constitutes the real necessity of dogmatic prolegomena.