On the Freedom of a Christian
On the Freedom of a Christian, sometimes also called "A Treatise on Christian Liberty" (German: "Von der Freiheit eines Christenmenschen") (November 1520), was the third of Martin Luther’s major reforming treatises of 1520, appearing after his Address to the Christian Nobility of the German Nation (August 1520) and the work Prelude on the Babylonian Captivity of the Church (October 1520). This work was originally written in Latin then translated into German and developed the concept that as fully forgiven children of God, Christians are no longer compelled to keep God's law; however, they freely and willingly serve God and their neighbors. Luther also further develops the concept of justification by faith. In the treatise, Luther stated, "A Christian is a perfectly free lord of all, subject to none. A Christian is a perfectly dutiful servant of all, subject to all." 
- Albrecht Beutel, "Luther's Life," tr. Katharina Gustavs, in The Cambridge Companion to Martin Luther, ed. Donald K. McKim (New York: Cambridge University Press, 2003), 11.