violated what Copernicus considered a basic axiom in astronomy. Ptolemy had created a device to account for the planets’s changing brightness and speed that violated the principle of perfect circular motion, and so Copernicus was looking to rectify that.  The Arabic astronomers of the 13th and 14th Centuries had found the same problem with Ptolemy, and they matched or improved Ptolemy’s methods by changing the math.  It’s more than likely that Copernicus, probably while he was a student in Italy, saw manuscripts showing the work of those Arab astronomers, because some of his math is exactly the same.  (They saw no need to suggest the Earth and Sun switch places, as Copernicus did.)  
     Copernicus had no predecessor he knew of for a heliocentric system, so that was original with him, and he never explained what gave him that idea.  But when he did it, he got the immediate result of seeing the speeds of the planets line up in order, going out from the Sun.  That must have struck him with the force of a divine revelation.

Yet he very well could have kept this idea to himself.  There was the fear of being ridiculed, but how much of that stemmed from the religious climate at the time?
The ridicule could have come from anybody, from the most uneducated person he dealt with in his work as a cathedral administrator.  But the religious problem was the fear that someone might take a passage from the Bible and twist it to discredit him, and given the rise of the Protestant Reformation against the Catholic Church, he had even more to worry about.  With the church under attack, he couldn’t be seen to be doing anything to contradict the Bible.