"The Study of Divine Things": Kepler as Astronomer-Priest

In the town of Leonberg in 1581, the ten-year-old Johannes Kepler first dreamed of devoting his life to God. What he really wanted was to be a prophet. Even to this rather solitary dreamer, it was clear that the world desperately needed guidance, and as a prophet he would have direct access to God's plan for his wayward people. Yet he felt in his bones that he was too impure and knew that a life of prophecy was beyond him. If he could not speak to God, then, he would speak for him; he would become a Lutheran priest. Kepler pursued this dream for the next thirteen years, until, while he was completing his theology degree at the University of Tübingen, a letter arrived that was to change the course of his life. The Lutheran school in Graz required a new teacher of mathematics and requested that the faculty at Tübingen send along their best candidate. Kepler was their choice, and though he had no desire to teach mathematics (even though the subject was one of his great loves), he reluctantly agreed. After all, poor and dependent on the goodwill of his teachers, what else could he do?

In the years that followed, Kepler rose from his position as a lowly teacher and district mathematician to the post of imperial mathematician to the Holy Roman Emperor himself. Though this no doubt comforted the man still continually plagued by fears of poverty, what comforted him still further was the way he recast the position of astronomer so that it enabled him to fulfill his earlier dream. "I truly believe," he wrote, "that as astronomers we are priests of the Lord Most High with respect to the Book of Nature." As an astronomer-priest, he believed that he could use his mathematical talents for the good of God and his church. And he ultimately claimed that as an astronomer-priest he had been able to fulfill the earlier dream of prophecy that had seemed impossibly elusive — he had been able to read the mind of God.

In this chapter, I focus on Kepler's early conception of the relationship between his mathematical and astronomical work (his science, in modern parlance) and his confessional identity (his religion). In particular, I consider the ways that Kepler hoped to use his mathematical astronomy in the service of his particular understanding of true religion. First, though, some contextualizing is necessary, for what place reason and philosophy (including both metaphysics and natural philosophy) should have in theology — indeed, whether they should have a place at all — was a contentious issue in the Lutheran Church of the seventeenth century. Delimiting the boundaries between various disciplines and choosing what metaphysics, if any, should inform one's theological views also formed a dividing line between confessions. Philosophy and science, that is, were often marshaled as weapons in the tense and volatile confessional battles of Kepler's day.

This was particularly true for the issue central to Kepler's own disagreement with the Lutheran doctrine of his age: the nature of Christ's presence in the Eucharist. Varying understandings of Christ's Eucharistic presence formed one of the central dividing lines — and the harshest points of contention — between the three major confessions in the post-Reformation era. The debate revolved not just around Communion itself but also around the larger question of how Christ's two natures — divine and human — related to one another. When Christ had pointed to the bread at the Last Supper and proclaimed "this is my body," what did that mean? Was his presence in the bread and wine at each and every subsequent Communion real or symbolic, human or divine? Catholics traditionally relied upon the Aristotelian distinction between substance (or essence) and accident to explain the real presence of Christ in the Eucharist. According to this perspective, known as transubstantiation, at the moment of the Mass the substance of the bread and the wine transformed into Christ's body and blood, while their accidents — their external appearance — remained the same.

Like his Catholic predecessors, Luther agreed that Christ's statement "hoc est corpus meum" implied his real presence in the Eucharist, though he took issue with the Aristotelian categories with which Catholics framed the debate. Christ's body and blood were, according to Luther, actually present in the bread and the wine, even if attempting to parse that presence in philosophical terms was a hopeless task. Luther did insist, however, that the presence of Christ's body and blood was not restricted to the bread and the wine at the moment of Mass alone. According to Luther: "Because we believe that Christ is God and man, and the two natures are one person, so that this person cannot be divided in two ... it must follow that he ... is and can be wherever God is, and that everything is full of Christ through and through, also according to his humanity — not according to the first, corporeal, limited manner, but according to the supernatural, divine manner." On the basis of the doctrine of communicatio idiomatum, the communication of properties, Luther argued that all the consequences of Christ's divine nature applied equally to his human nature, since the two were one. As a result of this belief, Luther arrived at the doctrine known as ubiquity, referring to the omnipresence of Christ in both his divine and his human forms. This doctrine maintained that as God was omnipresent, so too was Christ's physical body to be found everywhere throughout the universe.

By extension, Luther did not assert a miraculous change of the substance of the bread and the wine into the body and blood, for Christ's body and blood were already there, as they were everywhere. The Mass was a powerful testament that Christ left behind for his followers, not a particular, localized miracle or transformation. Moreover, Luther argued that believers needed to refine their understanding of Christ's body and what its presence actually implied. Rather than a kind of pantheism, to which it steered dangerously close, Luther's doctrine of ubiquity maintained that Christ's body was not corporeal in the usual sense of the term, as it was not subject to any physical or natural limitations. Christ's body, according to Luther, was really present everywhere, but not locally so. The Eucharist did not link the body of Christ directly to the physical world, for the presence of Christ's body in the Eucharist could be understood in only a nonmaterial and nonlocal sense, as could the presence of Christ's body in the world more generally.

The Formula of Concord reinforced the Lutheran...