“Up to this very day the Spirit calls into being the existence of every single Christian as a believing, loving, hoping witness to the Word of God.  The Spirit does this certainly and irresistibly (for to wish to withstand him, when he steps in and acts, would be the one unforgivable sin), for he alone does this.”

Thus Barth considers resistance to the Spirit’s work, particularly in making believers witnesses to the Word, to be the unpardonable sin.  Since he apparently rejects the possibility of a true believer committing blasphemy against the Spirit, he concludes that the Spirit’s work in a believer’s live is ultimately irresistible.

Karl Barth, Evangelical Theology: An Introduction (New York: Holt, Rinehart and Winston), 55.