In this his most well-known volume, Williams, the first Baptist in America, argued against religious conformity and uniformity at a time when dissenters on both sides of the Atlantic Ocean were suffering harsh persecutions from theocratic regimes.
Williams argued for liberty of conscience and freedom of religion for all persons, including Muslims, Jews, and pagans. And he insisted upon the separation of church and state. In another work, Williams coined the phrase "wall of separation" to describe the proper relationship between church and state.
To say the least, Williams' views were heretical. Many of the original copies of The Bloudy Tenent were burned by his opponents.
Americans today know Roger Williams as the founder of the Rhode Island colony and modern democracy. Within Rhode Island, Williams and his allies (Baptist and otherwise; Williams himself remained Baptist for only a short while) enacted freedom of conscience, full religious liberty for all, and separation of church and state. Many decades later, the freedoms enacted in the Rhode Island charter became a model for the formation of the United States of America as a nation dedicated to freedom of conscience, religious liberty, and separation of church and state.
Baptists today can be thankful to Roger Williams for the freedom impulse he helped instill as a central part of our faith heritage.