Finish the game in Insane Mode without reloading the camerabattery
Messiah is an achievement/trophy in Outlast 2. To achieve it, the player must complete the game on Insane difficulty without reloading the camcorder's batteries. The difficulty has no checkpoints or saves, meaning that if the player dies, they will lose all of their progress and be forced to start from the beginning of the game.
In Abrahamic religions, Messiah is a person chosen to lead the world and thereby save it.