The Plan of "Union"

I'm currently re-reading Seeking a Better Country: 300 Years of American Presbyterianism by Darryl Hart and John Muether. Here's some of their thoughts on the 1801 Plan of Union, a plan proposed by Union Seminary president Jonathan Edwards, Jr. to unite Presbyterians and Congregationalists in the common cause of Christian ministry.

E. H. Gillett commented on the cooperation with Congregationalists as a reason for celebration because "at this crisis in the religious progress of our country such liberal and Christian views prevailed." He added that the great "struggle" of the century, namely, "to shape the future destiny of a growing nation," had begun, and it called for "the hearty cooperation, on broad principles, of all who loved the common cause."

But another way of looking at the Plan of Union, along with similar missions endeavors in the South, was to wonder about the identity of the Presbyterian Church. Presbyterianism in one part of the country could wind up with a form of Christianity that questioned some of the central tenets of Reformed theology. And in New York the same Protestant communion could agree to form a cooperation that seriously undermined the chief arguments for Presbyterian church government. In other words, the Plan of Union was an early iteration of a phrase that would gain great urgency later in the nineteenth century, "doctrine divides, ministry unites." Yet, if Presbyterianism were so malleable as the conditions of the church indicated during the first two decades of the nineteenth century, what made the Presbyterian Church U.S.A. Presbyterian (emphasis added, 103-04)?