This article consists of four parts. In the first part that is entitled the “Word of Lord in the mother tongue of the Masurians”, the author stresses the importance of a sermon delivered by Jerzy Polentz – the bishop of Samland and the first Lutheran bishop in history – in the royal cathedral on 24 December 1523, in which he admonished that the Word of God should be preached in the native tongue of the believers, in the case of Masurians – the Polish language. The second part, entitled “Official introduction to Lutheranism in the Duchy of Prussia”, discusses the documents issued by Prince Albrecht, in which he established the principles of faith and conduct in the Lutheran Church of the Ducal Prussia. These included: 1. “Reformation Mandate” of 6 July 1525, demanding that priests preach “pure” Word of God, which according to the contemporary terminology meant preaching the Gospel based on the teaching of Martin Luther; 2. “Church Ordinance” and “Agenda or articles about ceremonies”, both documents published on 10 December 1525; 3. “Visitation instruction” of 13 March 1526, containing regulations regarding the transformation of Catholic parishes into Lutheran ones. The third part is entitled “Polish pastors in Masuria” and lists the names of first Lutheran priests active in the southern part of East Prussia. They were usually former Catholic priests who converted into Lutheranism. Many of them were Polish. Finally the fourth part entitled Polish Lutheran books in Masuria” is devoted to Polish religious prints (Catechism, New Gospel, Posil, Augsburg Confession, etc.). The author quotes here Władysław Chojnacki who claimed that more Polish prints were published in the 16th century in the Ducal Prussia (Königsberg and Lyck) than in entire Poland: 104 prints appeared in Polish, 183 in German and 90 in Latin. Most of them contained Lutheran religious writing. Usually, one parish owned at least a copy of the Bible, Postil, Catechism and a Polish Hymnal. One copy of Catechism allowed the community of believers to learn the Ten Commandments, while one copy of Hymnal enabled them to memorise many sacred songs.