The adoption of James Freeman's revised prayer book by Boston King's Chapel was a pivotal moment in American religious history. The revised prayer book, which eliminated the Nicene Creed, indicated a notable shift toward Unitarian theology—a movement that emphasized individual reason and a more personal interpretation of Christian doctrine. James Freeman, the minister at King’s Chapel, was a key figure in this transition. His innovative approach attracted a congregation that sought a more rational understanding of faith, diverging from the conventions of traditional Christian denominations that adhered strictly to Trinitarian beliefs.

Boston King's Chapel, initially an Anglican church, embraced this transformation during a period marked by the Enlightenment, where reason and scientific thinking began to influence spiritual beliefs. The decision to adopt Freeman’s prayer book in 1785 not only shaped the church's doctrine but also signaled the emergence of Unitarianism as a distinct branch of Christianity in the United States. This move was significant as it represented a broader trend toward liberal theology in America, where congregations began to question orthodox doctrines in favor of a more subjective form of worship and spirituality.

As a result of this change, Boston King's Chapel became the first Unitarian congregation in the United States. This new religious identity laid the groundwork for subsequent Unitarian and Universalist congregations across the country, ultimately contributing to the broader movements of religious liberalism. The church also became a focal point for theological debate and the spread of Unitarian ideas, influencing the course of American religious thought in the years to come.