The Anglican ideal in 1559 was liturgical and organizational uniformity in a national church; today it is a comprehended diversity in a global communion. This very familiar generalization points in the right direction, but it requires a number of qualifications. One is that each Anglican province processed this shift in its own distinctive way, in its own time, and with its own specific purposes. In many places, Anglicans came to accept diversity only after generations of ferocious debates, partisan church politics, and lawsuits. In the case of Scottish episcopalianism, diversity was thrust upon it in a whirlwind in the decade or two after 1689, and its biggest problem for the next three centuries was not to keep its warring factions within, but to reunite its fragments. It achieved this historic goal in 1988 when St. Thomas's Church, an outpost of English evangelicalism in Edinburgh dating back to 1842, finally joined the Episcopal Church of Scotland.
What originally brought serious diversity to Scottish episcopalianism was the dissolution of its authority structure in 1689. The Church of Scotland had been episcopally governed since 1662, but at the Revolution which brought William and Mary to the throne, the Scottish bishops, to a man, maintained their loyalty to the Stuarts. (The Stuart kings were, after all, not only champions of episcopacy but also descendants of the ninth-century Scottish king Kenneth MacAlpine.) The bishops thus gave the government no real choice but to end episcopacy and to restore presbyterianism to the Church of Scotland. From then until 1792, the bishops lacked any legally enforceable jurisdiction, and therefore each episcopalian meeting-house was left to determine its own life, congregationalist-style. Some congregations used a version of the Scots prayer book of 1637, others the English prayer book of 1662, and probably most, at least until the 1740s, followed an order of service little distinguishable from the Presbyterian. In the 1720s and 1730s some congregations recognized the "college" bishops who had no diocese, while others recognized the diocesan bishop, and still others recognized no bishop at all. Episcopalians in the "qualified chapels", which were recognized by statute and repellent to the bishops, were required to pray for the recognized monarch; others risked arrest by praying for the Pretender James VIII (or later Charles Edward). Among the latter, some acknowledged the Pretender's royal prerogative to govern the Church, but some did not. From time to time, leaders of the rival parties met together to seek peace.
After the death of the Young Pretender in 1788, the Scottish Episcopal Church secured full legal toleration and its bishops could exercise authority, albeit no longer in an established church. But unity remained elusive. Not only did some "qualified chapels" remain independent, but, in addition, they served as a ready model for new congregations which liked episcopacy in principle but disliked bishops in practice. Of these new congregations, St. Thomas's, Edinburgh, was the most important.
St. Thomas's originated in what historians have variously called, depending on their position on the ecclesiological spectrum, the Drummond Schism, the Diminuendo secession, or the Drummond Controversy. Its best historian is Rowan Strong, in Episcopalianism in Nineteenth-Century Scotland (Oxford, 2002). David Thomas Ker Drummond, an Oxford-educated Scot, was rector of an Episcopal church in downtown Edinburgh. In 1838 he began leading weeknight evangelistic services. Scottish episcopalians, overwhelmingly highchurch, scarcely knew what to make of this, and Drummond's bishop cited him in 1842 for deviating from the text of the Prayer Book in public worship. Drummond resigned from the diocese, and he and his supporters formed "St. Thomas's English Episcopal Church," which they viewed as a kind of ecclesiastical peculiar of the Church of England. It used an English liturgy and came to attract English immigrants. …