Protestants are told the scriptures are self-authenticating; because the scriptures are God’s word, they have the power to convince us of their truth. Johann Gerhard writes: “Because it is God-breathed, published, and spread by divine inspiration, therefore it is credible in itself, having credibility from itself.” David Scaer simplifies this thought: “Because the biblical writers were recipients of immediate illumination, the Bible possesses a self-authenticating authority.” Thus the Bible is “credible in itself, having credibility from itself”; thus the Sacred Scriptures are “self-authenticating”, whole unto themselves, needing nothing external to themselves as witness to their inspiration. While this makes sense in terms of the Protestant antipathy to Rome, they fail to realize the concept of self-authentication makes the Scriptures into a demiurge, a created god. Not God in essence, not a fourth person of the Trinity, but much more than an ordinary created being. The Gnostics (and others) described this type of lesser god as a demiurge. The idea that the Sacred Scriptures are “self-authenticating”, that their credibility is intrinsic, elevates the Scriptures above all other creation, and effectively denies the person and the extrinsic witness of the Holy Spirit. The author of Hebrews says “the word of God is quick, and powerful, and sharper than any twoedged sword, piercing even to the dividing asunder of soul and spirit, and of the joints and marrow, and is a discerner of the thoughts and intents of the heart.” (Heb 4:12) However, we are to understand this passage as a description of the work of the Holy Spirit in the world, in the Church, and in the heart of each human person. We know this directly from the words of Jesus Christ, when He spoke of the work of the Holy Spirit. “But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you.” (Jo 14:26) And again: “But when the Comforter is come, whom I will send unto you from the Father, even the Spirit of truth, which proceedeth from the Father, he shall testify of me.” (Jo 15:26) Either the Holy Spirit is our guide to understanding the Sacred Scriptures, or the Sacred Scriptures are a witness unto themselves, with no God necessary. You can’t have it both ways.
Gerhard, Johann. On the Nature of Theology and Scripture. Translated by Richard J. Dinda. St. Louis: Concordia Publishing House, 2006.
Scaer, David. “Baptism as Church Foundation.” Concordia Theological Quarterly 67, no. 2 (April 2003): 109-129.
 (Gerhard 2006, 68)
 (Scaer 2003, 118)