Everlasting Torment

Spells and abilities that would normally cause a player to gain life still resolve, but the life-gain part simply has no effect.

If a cost includes life gain (like Invigorate's alternative cost does), that cost can't be paid.

The "damage can't be prevented" statement overrides all forms of preventing damage, including protection abilities. Damage prevention spells and abilities can still be cast and played; they just don't do anything.

Effects that would replace gaining life with some other effect won't be able to do anything because it's impossible for players to gain life.

Effects that replace an event with gaining life (like Words of Worship's effect does) will end up replacing the event with nothing.

The last ability affects all damage, whether it's dealt by creatures, other permanents, spells, or cards that aren't on the battlefield. Wither works everywhere.