The year 1522 was a crucial year in the Reformation of preaching, with Ulrich Zwingli advancing the scripture principle—sola scriptura—in his "Clarity and Certainty of the Word of God" and Johannes Oecolampadius, just a few months prior, making a simple change to the mass that provided for the audible reading of, and preaching from, Scripture in the local language. His rationale: that Jesus desires to speak plainly to his disciples and that Paul emphasizes the intelligibility of divine revelation in worship; the grounds for this (at the time) seemingly radical change is God's love for and presence among those to whom he would reveal himself, yes, through the human activity of reading and preaching the Word. This Sermon on the Vernacular was promptly published in both Latin and German, along with the letter, from Caspar Hedio, inquiring into the changes that had become the subject of much gossip, and with Oecolampadius' "beautiful letter" in response. The sermon itself was preached on the Ebernburg, where Oecolampadius, serving as military chaplain for some months under the protection of Franz von Sickingen, saw himself "sowing on rock." The year 1522 was likewise crucial for Oecolampadius himself, finally clinching his breakthrough to the Reformation. It began with his flight from the monastery, saw him through a productive asylum in which he first came under the influence and began to translate the sermons of Chrysostom, led him to the "rocky" service on the Ebernburg, and culminated in his final relocation to Basel, where he would soon emerge as the city's chief Reformer, and in his famous overture of friendship to Zwingli. Throughout the year, the one figure with whom he corresponded most frequently, however, was Hedio, with whom his conversation returned again and again to proclamation. Now, at the 500th anniversary of its initial preaching and publication, this Sermon on the Vernacular and the letter explaining it finally appear in English for the first time, along with the balance of Oecolampadius' 1522 correspondence, and subsequent communications with Hedio, including Hedio's topical Foreword to his German translation of Oecolampadius' Sermons on the First Epistle of John. A generous Supplement is offered here as well, including Ernst Staehelin's monumental 1916 essay on Oecolampadius' translations of the patriarchs.