The Westminster Assembly was established in response to the growing dissent and the desire for ecclesiastical reform in the Church of England. As the English Civil War unfolded, tensions between King Charles I and Parliament escalated, particularly over the King's perceived overreach in religious matters and governance. In 1643, Parliament convened the Assembly at Westminster Abbey, marking a critical moment in English religious and political history, aiming to address issues such as theological disputes and administrative structure of the church.

Although King Charles I initially sought to maintain control over the church's governance, the Assembly operated independently from royal authority, reflecting the shift in political power towards Parliament. Comprising prominent Puritan theologians and various parliamentary members, the Assembly produced the Westminster Confession of Faith, a crucial document in Reformed Christianity, which articulated Calvinistic theological principles and rejected aspects of Anglicanism.

The decisions made at the Assembly had significant implications for the future of the Church of England and set the stage for further religious conflicts throughout the 17th century, including the emergence of different denominations and sects within Protestantism. The fruits of their labor were not merely confined to academic discussions; they influenced the religious landscape of England and shaped the policies of the Commonwealth following the execution of Charles I in 1649, during which many of these reformation ideas would be put into practice by the Puritan-led government.