In the sixteenth century, the Scottish and English reformations parted ways. Whereas Scotland enjoyed relative success in reforming church and state, Edward VI's death arrested England's reformation. When Protestantism was restored after Mary I's death, further reformation was not on the agenda of Elizabeth I, James I or Charles I. By the late 1630s, long-standing tensions burst into the open after a royal intrusion into the theology and practice of the Scottish Presbyterian Church led the Scots to march into England (the Bishop's Wars of 1639–1640). These wars helped bring England's parliament into open conflict with their king. Then military cooperation between Scotland and England's parliament laid the groundwork for a theological union. Although the Westminster Assembly of Divines worked to bring about theological concord, uniformity remained elusive. It was natural for Scotland to believe that their purified church would provide the template for England, and the Solemn League and Covenant even made this an aim of military cooperation (an agreement with loopholes).

Puritan theology fragmented as the godly entered the daylight. Victory and defeat facilitated this splintering. ‘Puritanism’, wrote John Morrill, ‘both triumphed and disintegrated in the English Revolution’. The Westminster Assembly of Divines, noted Chad Van Dixhoorn, experienced a similar rise and decline:

Given the political and religious fragmentation, one sub-theme in this book is that there was no authoritative interpretation of victory.

To the frustration of Presbyterians, they were only one of many voices trying to interpret providence and reform England. New Englanders returned to Old England and assisted parliament. Many articulated an alternative vision for a purified church – Congregationalism. Unity and purity, again, pulled in opposite directions. As Michael Winship has argued, ‘the wound Congregationalism created in English Puritanism would never heal’.