Over the last few years, following my grandparents’ decision to downsize and move into an assisted-living community, my family has been sorting through a treasure trove of documents to piece together our ancestors’ story. As we’ve explored the letters and records left behind by our forerunners, perhaps the most prominent theme that comes through is their deep commitment to their Lutheran faith. In fact, we think they originally fled Europe in search of religious freedom in America.

The driving force behind their emigration was the Prussian Union, a forced consolidation of Lutheran and Reformed churches in Germany by King Frederick William III. Unwilling to compromise core Lutheran distinctives for the sake of superficial ecclesial unity, many of Germany’s Lutherans—including those who went on to found the Midwestern-centric Missouri Synod—chose to live out their faith in a new land.

Ruptures always leave scars, and the Prussian Union controversy was no exception. While reading about this event, I stumbled down a historical rabbit hole and came face-to-face with a particular theological concept that bedevils American Lutheranism to this day: the notion of the “sin of unionism.”

You’d be forgiven for not knowing what “unionism” refers to—I certainly didn’t. According to the Lutheran Cyclopedia, “unionism” refers to “various degrees of coorganization, joint worship, and/or cooperation between religious groups of varying creeds and/or spiritual convictions.” Per the Missouri Synod’s constitution, this can mean “[t]aking part in the services and sacramental rites of heterodox congregations or of congregations of mixed confession” and “[p]articipating in heterodox tract and missionary activities.”

In recent years, the highest-profile cases of alleged unionism have involved participation by LCMS clergy in ecumenical worship services, including a 9/11 prayer event and a vigil following the 2012 mass shooting in Newtown, Connecticut. The offending pastors were required to apologize under threat of administrative sanction. And the synod’s anti-unionism language is not limited to pastors: perhaps this is the lawyer in me talking, but under a particularly aggressive interpretation of the unionism definition, I was in violation of the LCMS constitution every time I attended nondenominational chapel services at my (Christian) college. (In fact, I’m probably in flagrante delicto merely by writing for this website of mixed Christian perspectives.)

As one might expect, the various schisms in confessional American Lutheranism that have been spawned by accusations of “unionism” are the stuff of black comedy. The Wisconsin Evangelical Lutheran Synod (WELS) split from the LCMS on the theory that any common worship at all with non-Lutherans (even prayers before meals!) constituted sinful unionism. Shortly thereafter, the Church of the Lutheran Confession (CLC) split from WELS on the theory that participation in the same insurance association with non-WELS Lutherans constituted improper unionism. The Lutheran Conference of Confessional Fellowship then split from the CLC on the theory that the CLC was insufficiently zealous in punishing said “insurance unionists” by allowing for the “continued communing of those who were being admonished but had not given up their membership in these organizations.” In other words: CLC members didn’t drop their sinful insurance coverage fast enough, so they should be excluded from the Lord’s Table. Enough said.

In fairness, there’s a kernel of legitimate concern at the heart of this schismatic saga. It isn’t hard to see that the fear of unionism is rooted in the long-ago specter of the Prussian Union. Lutherans’ rejection of that merger makes sense: the Lutheran and Reformed traditions really are different in meaningful ways (most crucially in their sacramental theologies). The Lutherans who left Germany reasoned (rightly) that they could not abandon their convictions about the means of grace at the behest of a secular ruler.

But it strikes me as a serious overcorrection to transmute that concern into a species of “sin” never identified in Scripture, particularly in light of Christ’s prayer for the Church “that they may all be one.” And there is a special irony here, given that Lutherans like to define themselves against Catholics by rejecting the perceived tendencies of the Roman Church to adapt its doctrine to historical contingencies. Yet that same move takes place when the rejection of the Prussian Union becomes the “sin of unionism.”

Moreover, the broader Christian tradition has not held the restrictive position that unity in all points of theology is necessary for real fellowship to take place. Consider, for instance, the development of different approaches to Christology by the Antiochene and Alexandrian theological traditions, which culminated in the Council of Chalcedon in A.D. 451. Despite real differences in doctrine—differences far weightier than whether or not to participate in a common insurance organization—the Alexandrian and Antiochene Christians were able to come together, affirm one another as brethren in the faith, and contribute to a common project of doctrinal formulation. Yet such an act would be unthinkable under the approach to unionism favored by a not-insignificant number of American Lutherans.

This isn’t to say that some degree of separatism, at some point, isn’t important. The preservation of any institutional identity over time requires both boundaries and a willingness to police those boundaries. For instance, it strikes me as odd that the Evangelical Lutheran Church in America (a pillar of mainline Protestantism) acknowledges the “mutual recognition and availability of ordained ministers” and “exchangeability of members” with the Presbyterian Church (USA), the Episcopal Church, the United Methodist Church, and the United Church of Christ—given the radically different theologies underlying each denomination. Even in that case, though, I fail to see how joint worship activities would prove sinful in themselves. Rather, this seems to me to be a case of prudence. Making denominational boundaries that porous sends the message that longstanding disputes of theological significance—for instance, whether Jesus’ body and blood are really present in the Sacrament of the Altar—really don’t much matter after all. To avoid sending that message, it strikes me as prudent to maintain some lines between traditions. But that conclusion is a far cry from labeling line-blurring the “sin of unionism.”

Hopefully, confessional Lutheranism in America will eventually be able to exorcise its fears of the Prussian Union, and move towards healthier relationships with other confessional traditions. (Recently, I’ve been particularly happy to observe the fruitfulness of ongoing talks between the LCMS and the Anglican Church in North America [ACNA]). The real threats faced by confessional faith in America—an atomizing secularity that sees traditional religious convictions as structures to be demolished, and a growing population of citizens that simply don’t care about “first things”—have nothing whatsoever to do with interdenominational cooperation.

The hour is later than that.