It is a tale about power and politics and it is close to the Greek tragedy where there is no right choice. It is about Religion and about State - but there are no references to the history of Poland and the particular relation of Catholic Church and the Polish State. Please do not force it into a shape that it does not fit at all.
And by the way the characterization of the priests as corrupt is a misunderstanding - this is only how the immature and rather shortsighted main character sees them.
I have seen that film many times, since it is replayed quite often by the public TV here, I loved it's style since the first time - but I regarded it as a rather boring. It's only recently that I've found interest in it's main subject and that changed my attitude.