So basically it's the original root of the priest ( having both Divine and magical powers) views the world. My take is that she was either an experiment herself by her given birth or genuinely was born w it due to her parents lineage and was shunned bc of the "forbidden" mix match. The empress saw this as an opportunity to create an empire befitting for her own gains and the priest who hates ppl from the same background or superior to theirs agrees w the empress. Hence why they want to revert back.