Moth Priests believe it's their sacred duty to study the Elder Scrolls. They read them in order to divine the future and use the knowledge to aid the Emperor. Sometimes, they venture out into the world to search for more scrolls for the library in the White Gold Tower.
Moths Priests eventually become blind after reading from the Elder Scrolls, usually during old age. Dexion Evicus became blind early in his life because of haste when reading from an Elder Scroll.