Heretics cannot themselves appear good unless they depict the Church as evil, false, and mendacious. They alone wish to be esteemed as the good, but the Church must be made to appear evil in every respect.
Dictata super Psalterium (Dictations on the Psalter). This is Luther's first major work from the years 1513 to 1515.
As quoted in: Luther and Lutherdom From Original Sources, Volume 1 (1917), p. 15