The inclusion of Great Prophets transforms the mid-game, adding a layer of spiritual warfare that was missing from the base game.
: Unlike Missionaries, Great Prophets do not lose religious strength when entering foreign territory without open borders. This makes them "spiritual cruise missiles" that can erode and replace enemy religions in resistant cities. sid-meier-s-civilization-v-complete-edition-prophet
: Great Prophets are the only units capable of founding or enhancing a religion once you accumulate enough Faith (typically 200+). The inclusion of Great Prophets transforms the mid-game,