Nicolaus Copernicus's re-mapping of the macrocosm wasn't the only sixteenth-century breakthrough on a scientific frontier. Equally stunning was a bold trek into the microcosmic world of our physical selves.

This voyage, led by the anatomist Andreas Vesalius (1514-1564), seemed to bring humankind into a new and intimate knowledge not just of our physical being, but of our spiritual being as well.

Born in Brussels, Vesalius likely received his elementary education from the Brethren of the Common Life, a Roman Catholic spiritual association that trained Thomas à Kempis and Desiderius Erasmus. His studies took him from the great universities at Louvain and Paris to that at Padua, which appointed him professor of anatomy and surgery the day after he received his M.D. in 1537.

While at Louvain, Vesalius had participated in one of his first human autopsies, an event that set the course of his future research. The ancient anatomist Galen—rediscovered in the Renaissance—had derived his human anatomy from observations of animal subjects. But in his 1538 manual Six Anatomical Tables, Vesalius proclaimed a new method: researchers of human anatomy should dissect and observe actual human subjects, and develop terminology and illustrations to match their observations.

After 1539, Vesalius performed a series of dissections—usually on cadavers of criminals or indigents, or members of dedicated patron families. He recorded some of the results of these and sketched them for detailed rendering in the lavish woodcuts of his Fabric of the Human Body (1543).

Some anatomists reacted harshly, defending Galen. But most church leaders received Vesalius's findings without a murmur. (In fact, a notable 1540 dissection had taken place in Bologna's Church of San Francisco.)

When we read Fabric, we begin to understand this favor of the church. In the first chapter, Vesalius exults over the created wonder of bones: "God, the supreme Architect, in his wisdom formed material of this temperament, placing it beneath the surface as a foundation for the whole body." In Book II, he urges his reader to "sing hymns to the Creator of the world, who produced from such a tiny space [the jaw muscle] in charge of such an important task." In Book VI, he passes over the question of why so much water flowed from the side of the crucified Jesus, "for I must not in the slightest degree upset the complete veracity of the authentic Gospel of John."

Vesalius's theologically informed approach to anatomy was not unusual in his time. Many sixteenth-century researchers studied the body to gain insight into the soul. Indeed, anatomy entered the curriculum of Lutheran Protestant schools not through medical schools but as part of the study of philosophy. And the man who introduced anatomy to the University of Wittenberg's curriculum in 1535 was a theologian—Philip Melanchthon (1497-1560).

Melanchthon admired Vesalius's work and shared his sense that this new, inner frontier bore the stamp of divinity. The theologian wrote this poem in his copy of Vesalius's Fabric:

"Think not that atoms, rushing in a senseless hurried flight,
Produced without a guiding will this world of novel form;
The mind which shaped them, wise beyond all other intellects
Maintains and fashions everything in logical design …
Accordingly it follows that the body's several parts
Came not together aimlessly as if devised by chance:
With purpose God assigned to each its own allotted task
And ordered that man's body be a temple to Himself …
Wherefore as man reflects upon the marvels in himself,
With reverence let him venerate this Maker and his Lord,
And keep the temple undefiled, immune from any stain,
Lest wrath divine in vengeance come and hurl it crashing down."

In 1564, following two decades as imperial physician, Vesalius, the "father of modern anatomy," died during a pilgrimage to the Holy Land.

Another who delved deeply into the theological meanings of "the body's several parts" was Spaniard Michael Servetus (1511-1553). Servetus is usually seen by church historians in light of his 1531 book On the Errors of the Trinity—in which Melanchthon found "many marks of a fanatical spirit." Historians of anatomy, on the other hand, cite his 1553 work, The Restitution of Christianity. In this book Servetus, who had studied and gained favor from the same Paris anatomy professor as Vesalius, became the first person to describe the "pulmonary transit" of blood through the lung from the heart's right ventricle to the left auricle. However, this ground-breaking discovery remained unknown to medical contemporaries, as the book was read by few (none anatomists) before it was condemned and burned with its author on October 27, 1553 in Calvin's Geneva.

Obsessed with the oneness of God, Servetus used his medical studies to stretch the biblical idea of God's omnipresence beyond its traditional bounds. He came to believe not only that God was the creator and sustainer of the material world, but also that the very air one breathes is a form of God Himself. Thus to his notorious preaching against the Trinity he added what seemed to many Christians a pantheistic teaching.

Servetus wrote of "the divine philosophy which you may easily understand if you have been trained in anatomy." He read in the body the structures and pathways of the Spirit, declaring "The matter of the soul (anima material) is made from the blood of the liver … the soul itself is the blood. … For the soul is not said to be principally in the walls of the heart or in the body of the brain or of the liver, but in the blood, as God Himself teaches in Genesis 9, Leviticus 17 and Deuteronomy 12."

Though each read it differently, Vesalius, Melanchthon, and Servetus joined others of their time in "returning to the text"—the text of the human body—in search of Truth both scientific and spiritual.

James D. Smith III teaches at Bethel Seminary, San Diego, and the University of San Diego. Special thanks to Cheryle A. Redelings of the Francis Parker School for her material assistance.