Any religion would loath heretics far more than any other enemy. Traditionalists would feel that the heretics' explanations of doctrine and new inventions would cause the religion to lose its "purity and tradition," needlessly confusing loyal believers.
An analogy would be the most frightening disease back on Earth—cancer. Ordinary cells would mutate and spread at a scary rate. Once the changes within one's body spread to a certain degree, it would be impossible for that person to remain alive. For the ones who battled and defeated cancer, it would put great strain upon their body.
In this world of True Gods, heretics were those with different understandings and explanations of the True Gods' teachings. This could cause changes in a Divine Concept or people's belief.
