The Word of God is certain and can never fail. It is clear, and will never leave us in darkness. It teaches its own truth. It arises and irradiates the soul of man with full salvation and grace. It gives the soul sure comfort in God. It humbles it, so that it loses and indeed condemns itself and lays hold of God.

—Ulrich Zwingli
Huldrych Zwingli, “Of the Clarity and Certainty of the Word of God,” in Zwingli and Bullinger, 93.