The corrupted power which fell to earth after the death of gods caused a huge plague of undead. Some are mindless or nearly so, zombies and skeletons, shells of bodies animated by pure corruption. Some however are not.
When one who touches the Blood embraces its potential, knowingly uses the corrupt power it can provide, and properly prepares oneself for the changes that are to come, it is possible to survive the corruption by enduring a tremendous transformation, and becoming one of the intelligent beings known as "blessed" due to their connection to the blood of the dead gods.
The Blood of the Gods inevitably causes corruption, physical and mental, and the Blessed each in some way feed off of the life force of the living.