Edit Szegedi has provided a valuable account of Anti-Trinitarianism in the Transylvanian principality during the second half of the sixteenth century. Using a wide range of manuscript and printed sources, Szegedi pieces together the Anti-Trinitarian struggle to pursue worship of the one true God in Transylvania. Szegedi explores with admirable clarity the complex ideas put forward by different Anti-Trinitarian preachers. She also situates the evolving character of the Anti-Trinitarian Church within the shifting politics of Transylvania. Sixteenth-century Transylvanian Anti-Trinitarians left a legacy without parallel elsewhere in Europe. Anti-Trinitarians were able to secure legal recognition for a Unitarian Church that has endured to the present day. However, as Szegedi argues, this undoubted achievement does not really match the expansive vision of early reformers. Anti-Trinitarians did not merely seek to set up a local institution but to reform Christian religion on biblical foundations. However, even this goal did not encompass the ambition of some thinkers who sought to reconcile Anti-Trinitarian Christianity with other monotheistic religions. These ideals were not abstract visions pursued in isolation by individual intellectuals but related to debates about religious life in Transylvanian communities. Nor were these ideals entirely abandoned within the Unitarian tradition in Transylvania, not least among Sabbatarians who attempted to combine Jewish and Christian religious practices.

Transylvania's Anti-Trinitarian tradition emerged from theological debates between Reformed preachers and writers in the 1560s. The ruling prince, János Zsigmond Szapolyai, offered vital support that encouraged the Anti-Trinitarian movement. Transylvania in the late 1560s and early 1570s became a centre of radical theological inquiry. Alongside domestic voices, exiles were drawn to Transylvania to preach and teach. Debate among reformers centred on different understandings about the person, character and authority of Christ. Was Christ best understood as a spiritual teacher or should Christ be worshipped, adored and invoked in prayer? Internal divisions reflected a lively culture of biblical inquiry but also posed a severe risk to the Anti-Trinitarian cause. A central theme of Szegedi's book is tracing the evolution of laws on religious rights as agreed by Transylvania's diet. In 1568 all ministers who preached their understanding of the word of God were granted legal protection. The effect of this provision offered rights to Anti-Trinitarian, Lutheran and Reformed preachers, but maintained an earlier ban against Catholic priests (who were deemed not to preach the Gospel). After the death of János Zsigmond Szapolyai, restrictions were introduced under the new prince István Báthory (who was also elected king of the Polish-Lithuanian Commonwealth). Existing churches and ministers were told not to indulge in any doctrinal innovation. In practice, this law was primarily directed against non-adorantist Anti-Trinitarianism. Szegedi provides very detailed analysis of the legal context of Anti-Trinitarianism from the 1560s as a ‘nameless’ religion. The legal position of the Church can only be inferred from the text of laws until 1595. Then, the diet clarified that Transylvania had four legal or received religions (described as Catholic or Roman, Lutheran, Calvinist and Arian).

The career of Ferenc Dávid (or Franz Hertel) is also prominent in Szegedi's account. Dávid was raised a Catholic in the town of Cluj. By the 1540s he was a Lutheran preacher and returned to Cluj to become superintendent of the Transylvanian Hungarian-speaking Lutheran Church (the German-speaking Saxon Church had a separate superintendent). For Dávid, as for many in the elite of Cluj, speaking both German and Hungarian was a part of their identity. Dávid straddled the reception of religious ideas in different linguistic communities, and by the early 1560s he had embraced Reformed religion and was superintendent of the largely Hungarian-speaking Reformed Church. In the mid-1560s Dávid began to question the biblical basis for orthodox Trinitarianism, and his voice was certainly significant as Anti-Trinitarianism came to dominate religious life in Cluj. Szegedi focuses on the remarkable urban Reformation in Cluj. The town became a refuge for thinkers such as Jacobus Palaeologus, who was engaged in a search for a syncretism of monotheistic religions. From German Reformed backgrounds, Adam Neuser and Matthias Vehe-Glirius also moved to live and teach in Cluj. Vehe-Glirius published a work on the knowledge of God that combined Jewish and Anti-Trinitarian ideas and literature.

Debates and disputes continued to bubble up among different Anti-Trinitarian writers and preachers about the nature of Christ and about whether the invocation of Christ detracted from the true worship of God. However, in 1578 the law against theological innovation was renewed and the city council of Cluj expelled Vehe-Glirius. In June 1579 Dávid was questioned about whether he accepted non-adorantism and had therefore broken the law against theological innovation. Dávid died while in prison, and Giorgio Biandrata drew up an adorantist creed for the Anti-Trinitarian Church. The church superintendents Demeter Hunyadi and György Enyedi then worked to legitimise this adorantist Anti-Trinitarianism as a Church operating within Transylvania's laws. More radical Sabbatarian voices were not formally expelled from the Unitarian Church until 1606. Szegedi indeed argues that the real winner from the confessional politics of this period was the Reformed Church. She traces how the small Reformed community in Cluj was able to secure control of the former Dominican church (then vacant). In challenging Unitarians in Cluj and elsewhere, the Reformed were quick to deploy the charge of Sabbatarianism to discredit their rivals. While the Unitarian Church maintained its legal rights as a received religion during the seventeenth century, as Szegedi writes the Reformed Church was fast becoming the first among equals in the practice of Transylvanian religious politics.