Self-Authentication of the Word of God

Following up on my previous post about Karl Bath and the conscience, I read an interesting chapter from William Lang Craig. In it, he explained that both Karl Barth and Rudolf Bultmann believed in the self-authentication of God's Word. Even though I already knew this, this sentence made Barth's comments on the conscience make sense to me. The conscience, enlightened by the Holy Spirit, through God's Word, is the only thing that can recognize God's Word as it really is.

The Conscience

I have been reading Barth's "The Word of God and the Word of Man." It's a wonderful read; very sermonic at times. However, it did raise a question that I have concerning Barth's view of natural theology.

In the introductory essay, given in 1916, Barth claims that conscience is "the only place between heaven and earth where the righteousness of God is manifest." This statement seems strange, coming from Karl Barth. Both the primary and secondary sources which I have read seem to state that Barth rejected any sort of natural theology.

I guess the question that needs to be asked is: how did Barth change from his early years (1916) to the later years (Christian Dogmatics)?