“The process of the reductio must be explained to him. There are two parts to the process. First the apologete must show that the axioms of secularism result in self-contradiction. … Then, second, the apologete must exhibit the internal consistency of the Christian system. When these two points have been made clear, the Christian will urge the unbeliever to repudiate the axioms of secularism and accept God’s revelation. That is, the unbeliever will be asked to change his mind completely, to repent. This type of apologetic argument … [does not] deny that in fact repentance comes only as a gift from God”
Karl Barth’s Theological Method, p. 110.