A canon of the Church and a staunch Aristotelian, Copernicus saw himself as returning to a more "pure" Aristotelian description of the heavens by eliminating ad hoc geometric constructions added by Ptolemy to his system. These constructs (the equants) violated the the fundamental Aristotelian insistence on uniform circular motion. To eliminate equants, but still "preserve appearances" (i.e., have a system that correctly predicted the motions of the planets), Copernicus revisited an old idea of Aristarchus of Samos that placed the Sun and not the Earth at the center of the Solar System. However, in attempting to preserve the past, he hastened its eventual downfall. But that was still well into the future.
For a "revolutionary" book, De Revolutionibus is anything but incendiary. It is written in a technical Latin style and contains intricate geometric arguments. Nor was it written as an open challenge to the Church or its authority. Far from it. The original edition, in fact, was dedicated to the current Pope at that time (Paul III), and it was printed with official sanction (an Imprimatur or official license granted by the ecclesiastical censor; a fact usually lost on a number of popular historical accounts). In general, it was considered by most to mainly represent a point of argument among "mathematicians," not an idea with any currency among the largely illiterate rank and file. Since it posed no immediate dangers to the faithful, it was ignored. The Church had weathered many a "secular novelty" in its time (to use Boorstin's phrase), and this was no exception, at least so it seemed in the middle of the 16th Century.
De Revolutionibus has often been called "the book that nobody read". Recent scholarship by Harvard historian Owen Gingerich has clearly refuted this. Many of the extant copies of first editions of Copernicus that Gingerich has examined contain extensive marginal notes written by their readers, showing that the ideas generated thought and discussion, both for and against. Scholars were not only discussing these ideas, but exploring their implications. One particular implication of the Copernican model (one not espoused by Copernicus himself) that it allowed (or at least did not explicitly rule out) a Universe that was infinite in extent. This idea appears to have been first broached in writing in the context of the Copernican model by the Englishman Thomas Digges in 1576 in his A Perfit Description of the Caelestial Orbes, and was of course an idea famously taken up by Giordano Bruno in the 1580s. While the number of people who had direct contact with De Revolutionibus was still relatively small, its influence was in fact considerable throughout the latter part of the 16th century and into the 17th century.
By the 17th Century, the Church's hands-off approach to the ideas presented by Copernicus and their deeper implications was no longer viable. The Catholic counter-Reformation that began as a response to Protestantism following the Council of Trent (1545-1563) was in full swing, and the embattled Church was on the offensive. A serious source of irritation to the Church was the rapid rise of printing and the accompanying increase in literacy, especially literacy in the vernacular instead of the scholarly language of Latin. This gave uncomfortable ideas a currency they didn't enjoy previously. For example, the Church would probably not have gotten so exercised by Galileo's Dialogue on the Two World Systems if it had been written in Latin instead of the Tuscan dialect of Italian. It also didn't help that Galileo's Tuscan prose was lively and engaging, and therefore brought these arguments to a wider audience in a style that made their underlying meaning crystal clear (even today Galileo is remarkably readable).
It was not until 1616 that the implications of Copernicus' ideas began to sink in and the Church responded by placing De Revolutionibus on the Index of Forbidden Books (the Index Librorum Prohibitorum) pending correction of minor points. Notice that this was not, at this point, an outright ban, but it did serve notice that the Church was uncomfortable with some aspects of the idea. As further illustration that it was not a formal ban, corrected editions of De Revolutionibus were soon in circulation at this time, carrying the imprimature of the official Church censors. While in the original deliberations by the Congregation of the Index the principles of "Copernicanism" were spoken of as heretical, the official declaration of March 5, 1616 stopped short of that, calling it instead "false and contrary to Holy Scripture". Another 48 years was to pass (1664) before the central ideas of the Copernican system were formally banned by papal decree as unfit for open discussion or teaching by the faithful. The response of the Church, while ultimately definitive and negative, was significantly delayed, in contrast to the nearly immediate reaction among Protestant leaders. The on-going reaction against Copernicus was also carried on primarly by the Protestants, especially in those parts of Europe under Protestant control. For example, the Ptolemaic system was taught at Harvard during its early days, as opposed to the godless 'romish' system of Copernicus (they didn't approve of his astronomy or his Roman Catholicism).
One specific anecdote that is often cited should suffice to illustrate the immediate Protestant reaction: Luther, in the collection of his conversations called the Table Books, once ridiculed Copernicus as "that fool who would go against holy writ" for suggesting that the Earth and not the Sun moved. This response seems based on word about Copernicus' idea that was being circulated during the decade or so before the actual publication of his book, not the book itself. While De Revolutionibus was a difficult geometric treatise that was read mostly by specialists, his ideas did make the rounds, primarily because of a "preview" of the system published as the short Commentariolus or commentary on the idea circulated privately, and later by the more detailed First Account of what was to become the larger work published by the itinerant Protestant astronomer and scholar Georg Rheticus.
The initial theological objections to Copernicus offered by Reformist (later called "Protestant") theologians, and even a few Catholic theologians, was that his system contradicted key passages of Biblical scriptures. There are two similar (but importantly distinct) doctrinal bases for these objections. The Protestant objection was based primarily upon a doctrine of strict "Scriptural Inerrancy," the idea that the Hebrew and Christian scriptures are the literally true, divinely dictated word of God. While we tend to regard this doctrine as one of the defining features of minority Christian Fundamentalist groups in the United States, it is often forgotten that a strong undercurrent of Scriptural Inerrancy was an important feature of much of early Protestant theology. A common touchstone of scriptural contention with the Copernican heliocentric system was a particular passage in the Old Testament in which Joshua commanded the Sun to stop in its course during a battle between the Israelites and the Amorite Kings (Joshua 10:10-15). In the heliocentric world view one would have to halt the Earth, but that's not what scripture said God did. This is the essense of what Luther was complaining about in the passage quoted above.
The doctrinal objection on the Catholic side was stated by Robert Cardinal Bellarmine in Galileo's time and was an amplification of an earlier doctrinal tradition that came out of the Council of Trent regarding the truth of scriptures. The traditional doctrine was framed by St. Augustine of Hippo in the 5th century AD in his De Genesi ad litteram libri duodecim. This doctrine held that where the words of scripture demonstrably contradicted the evidence of nature, they were to be treated as allegory or metaphor, but not literal truth. The implementation of this doctrine was guided by the concept of necessity. Essentially, the official teaching of the Catholic Church was that one was to treat scriptures a priori as literal, revealed truth unless necessity dictated otherwise. Thus, the Church had a framework in which to discuss conflicts between the accounts of scripture and the hard facts of the world around us, but it was quite explicit in its teaching that one was not to abandon the literal interpretation unless the evidence was so overwhelming that continued belief in the literal interpretation would constitute a perversion of divine truth. While the framework was in place, there was still considerable argument (which continues to this day) as to the mechanism to actually resolve conflicts when they arose. The subject is very complex and beyond the scope of this brief essay to explore.
The Catholic Church's official position on Copernicus was more nuanced than simply being a conservative appeal to scriptural authority as often portrayed. It is important to recall that the doctrine of strict Scriptural Inerrancy, at least as espoused in many Protestant circles at the time, was considered heretical by the Catholic Church, and an important point of contention with Protestant movements like those of Luther and Calvin. It was an important concept of Catholic theology, going back to the early church fathers, that a literal interpretation of scripture was only scratching the surface of the deeper truths, and to simply stop at the surface meaning was to risk falling into grave error. This is, incidentally, the primary Jewish approach to interpreting Scripture as well. Protestant sects that started out from a standpoint of strict literalism later found themselves forced to abandon this doctrine in whole or in part, in most cases because strict adherence to this doctrine inevitably leads one into serious logical inconsistencies, a problem that was to become especially acute in the 17th and 18th centuries when Biblical scholarship uncovered more reliable ancient source texts. Interestingly, modern mainstream Protestant ideas on the conflicts between scripture and science bear a more than passing resemblance to the doctrines outlined by Augustine and the earlier Church fathers, although their line towards establishing the burden of proof is less severe than that espoused by Bellarmine (and more akin to that used by, for example, Galileo).
The point of contention in the Church with the heliocentric world view was that it had not yet been demonstrated as a necessary interpretation of the world. While there was an interested "wait and see" attitude within the well-educated upper hierarchy of the Church, if they were questioned on the matter they would adhere to the scriptural account. "Interest" does not imply approval, and Bellarmine himself considered that Copernicanism was heretical, and adopted an especially conservative view of the matter. Bellarmine's approach was highly influential, and became the basis for the Church's response during the 17th Century. Before the matter became a point of serious contention (culminating in the trial of Galileo), the Church's argument was that this new idea, while interesting, was not yet sufficiently well established that it necessitated a revision of the traditional interpretation of scripture. Bellarmine went one step further and stated categorically that one could never prove the Copernican conjecture to the necessary level of certainty, and therefore the matter was closed. Galileo, by comparison, felt that it was an ultimately provable proposition (and felt that he himself had that proof in the form of a demonstration of the Earth's motion based on the phenomenon of tides that was, unlike other work of Galileo, incorrect), and therefore the matter was still open for discussion. Thus were laid the philosophical battle lines of his famous conflict with the Church over Copernicanism. We often focus on the scientific issues at hand, but in fact the deeper conflict was on deeply nuanced theological arguments about how one was or was not to test scriptural statements against the evidence in Nature.
If among the intelligencia of the Church there was guarded interest, the most vocal objection from within the Church came not from the hierarchy so much as the lower orders. In particular, there was a strong current of Scriptural Inerrancy prevalent among the less well-educated mendicant preachers, and it was among them that objections to the heliocentric system on scriptural grounds surfaced most publically. While Galileo's wide publication of his telescopic discoveries (1610) certainly catalyzed issues, it was the publication of a detailed theological defense of Copernicanism against the attacks of such preachers by Galileo's friend Paulo Antonio Foscarini in 1615 that precipitated the Church's official investigation into the controversy the following year (led by the same Cardinal Bellarmine who formulated the modern doctrine of scriptural interpretation noted above). Before 1616, the Church had made no official pronouncement on Copernicus. There followed nearly 50 years of controversy (bracketting the trial of Galileo for heresy in 1633), but it was not until 1664 that the Church made an explicit condemnation of the idea in a papal bull prefixed to the Index by Pope Alexander VII specifically banning ``all books which affirm the motion of the Earth''. It was to remain on the Index until the year 1835, when it was quietly removed from subsequent editions.
Copernicus' ideas even spread beyond academic circles. The most unlikely place was in the traditional "procession of fools" that took place as part of the celebrations leading up to Lent (a remnant of which remains to this day in the traditional celebration of Carnival in Latin countries, for example). This was a bawdy parody of the solemn religious processions that accompanied many high holy days. The characters who made up this procession were lampoons of all walks of life, and especially of members of the Church. After 1543, there began to appear among the latter a starry-eyed canon who kept tripping over his gown because he was always looking up at the sky instead of where he was going. The model is clearly Nicholaus Copernicus, the quiet canon of Frauenburg catherdral.