Book: Christianismi Restitutio

Overview
Christianismi Restitutio, published anonymously in 1553 by Michael Servetus, combines rigorous biblical exegesis with natural philosophy and medical observation. The Latin text advances a radical reinterpretation of Christian doctrine while interweaving anatomical and physiological claims that reflect Servetus's background as a physician and a humanist scholar. Its publication provoked immediate and violent controversy across confessional lines and became the focal point for Servetus's prosecution and execution for heresy.

Theological argument
Servetus rejects the traditional doctrine of the Trinity as a nonbiblical synthesis that obscures the singular divine nature. He argues that the scriptural witness points to one God who manifests himself in Christ and in the Spirit rather than existing as three coequal, coeternal persons. Emphasizing a strict monotheism, Servetus insists that Christ is the Son by participation and revelation, not a second person of an ontological Trinity; the Spirit functions as God's active presence rather than a distinct hypostasis. His method combines philological attention to biblical language, appeals to patristic texts, and philosophical argumentation, seeking to strip later creedal formulations of what he sees as philosophical accretions.

Critique of ecclesial authority
The book mounts a broad critique of both Roman Catholic and emerging Protestant institutions. Servetus challenges sacramental and doctrinal practices he views as corruptions of apostolic Christianity, and he rejects doctrines of sacerdotal mediation and compulsory creedal conformity. His polemical tone is uncompromising, and he singles out leading reformers for sharp rebuttal. That direct engagement with figures such as John Calvin escalated conflict and helped transform theological disagreement into a legal and political matter, particularly in the volatile confessional context of mid‑sixteenth‑century Europe.

Contributions to medicine and natural philosophy
Interleaved with the theological material are anatomical and physiological observations that mark Christianismi Restitutio as noteworthy in the history of science. Servetus offers one of the earliest clear descriptions of pulmonary circulation, arguing that blood moves from the right side of the heart through the lungs and returns to the left side, where it is then distributed to the body. He emphasizes the role of the lungs in transforming blood through contact with air, challenging the Galenic model then dominant in medicine. Though not a complete description of systemic circulation as later articulated by William Harvey, Servetus's account anticipates essential elements of modern cardiopulmonary physiology and illustrates the porous boundary between theological and scientific inquiry in the Renaissance.

Publication, persecution, and legacy
The anonymous 1553 edition was rapidly suppressed; ecclesiastical and civic authorities in both Catholic and Protestant territories condemned its doctrines. Servetus's denunciation of the Trinity and his open attacks on prominent reformers led to his arrest, imprisonment, and transfer to Geneva, where he was tried and executed by burning on October 27, 1553. Most copies of the book were publicly burned, but a few extant fragments and surviving copies preserved his arguments for later generations. Christianismi Restitutio influenced later nontrinitarian currents, including Socinianism and Unitarianism, and its medical passages are recognized as an important early step toward modern understandings of pulmonary circulation, securing Servetus a controversial but distinct place in both theological and scientific history.