Erewhon by Samuel Butler

In spite of all the to-do they make about their idols, and the temples they build, and the priests and priestesses whom they support, I could never think that their professed religion was more than skin-deep; but they had another which they carried with them into all their actions; and although no one from the outside of things would suspect it to have any existence at all, it was in reality their great guide, the mariner's compass of their lives; so that there were very few things which they ever either did, or refrained from doing, without reference to its precepts.

Now I suspected that their professed faith had no great hold upon them -- firstly, because I often heard the priests complain of the prevailing indifference, and they would hardly have done so without reason; secondly, because of the show which was made, for there was none of this about the worship of the goddess Ydgrun, in whom they really did believe; thirdly, because though the priests were constantly abusing Ydgrun as being the great enemy of the gods, it was well known that she had no more devoted worshippers in the whole country than these very persons, who were often priests of Ydgrun rather than of their own deities. Neither am I by any means sure that these were not the best of the priests.