Even Luther had not spoken with greater force against the abuses of Rome, but he had done something more. The duke pointed out the evil. Luther had pointed out both the cause and the remedy. He had demonstrated that the sinner receives the true indulgence, that which comes from God, solely by faith in the grace and merits of Jesus Christ. And this simple but powerful doctrine had overthrown all the markets established by the priests. “How can a man become pious?,” asked he one day. “A gray friar will reply, ‘By putting on a gray hood and girding yourself with a cord.’ A Roman will answer, ‘By hearing mass and by fasting.’ But a Christian will say, ‘Faith in Christ alone justifies and saves. Before works, we must have eternal life. But, when we are born again and made children of God by the Word of grace, then we perform good works.'”
From: A History of the Reformation of the Sixteenth Century by J. H. Merle D’Aubigne; translated from the French by H. White; reprint (Rapidan: Heartland Publications, 2006), p. 358 (Book 7, Chapter 4).