Abstract Adam Pastor was an itinerant Anabaptist bishop in the Lower Rhine region. Ordained by Menno Simons around 1542, he is best known for the division that unfolded between Dirk Philips and Menno Simons, which led to the first schism in Mennonitism. Although sixteenth-century contemporaries described him as an important bishop alongside Menno, Mennonite historiography since then has largely ignored him. Pastor’s theological views are known primarily from his Onderscheytboeck [ Book of Distinctions ] of ca. 1554. The recent discovery of an earlier and hitherto unknown version of this writing, however, demonstrates a more gradual development of Adam Pastor’s “spiritualism.” In 1547 Pastor opposed Menno’s Melchiorite doctrine of the incarnation. Several years later, he arrived at the inevitable conclusion and denied—at least implicitly—the Trinity. The result was his break with Menno and Dirk and a subsequent division between the bishops from the Northern Netherlands and those of the Lower Rhine.