In 1644, Williams published The Bloudy Tenent of Persecution. Historians consider it his most famous work. He wrote Bloudy after arriving in London in midsummer 1643. It was on sale by July 15, 1644. It is a fierce attack on religious and political intolerance in both Old England and New. He advocated for free thought and belief because he felt that punishing those that did not believe was not part of his faith and government should be separate from religion. Roger advocated for a “hedge or wall of Separation between the Garden of the Church and the Wilderness of the world” in order to keep the church pure. His ideas raised questions and challenges but his ideas endured over time.