In 1614, Leonard Busher wrote what is believed to be the earliest Baptist treatise dealing exclusively with the subject of religious liberty.
Messrs. Nehemiah Dodge, Ephraim Robbins, and Stephen S. Nelson A Committee of the Danbury Baptist Association, in the State of Connecticut.
Washington, January 1, 1802 Gentlemen, – The affectionate sentiment of esteem and approbation which you are so good as to express towards me, on behalf of the Danbury Baptist Association, give me the highest satisfaction.
Believing with you that religion is a matter which lies solely between man and his God, that he owes account to none other for his faith or his worship, that the legislative powers of government reach actions only, and not opinions, I contemplate with sovereign reverence that act of the whole American people which declared that their legislature would "make no law respecting an establishment of religion, or prohibiting the free exercise thereof," thus building a wall of separation between Church and State.
I reciprocate your kind prayers for the protection and blessing of the common Father and Creator of man, and tender you for yourselves and your religious association, assurances of my high respect and esteem.
1802[5] This doctrine, known as the "wall of separation" or "strict separationism," would later become highly influential in 20th century Supreme Court understandings of the relationship between church and state.
The relevance of this reply is a subject of heated debate, with scholars such as Robert Boston emphasizing its importance, and others such as Mark David Hall arguing that the letter was a historical outlier.