Revelation does nothing as of now. There are a number of magic skills that are useless at this point in the development of the magic system. It's supposed to grant you extra XP in some fashion but hasn't been totally worked out yet.
You gain XP by:
- Dealing damage
- Taking damage
- Exploring new rooms/levels
- Opening containers and chests
- Finding in game secrets
- Reading books
This is not an exhaustive list because the devs are purposefully keeping a lot of the back end info secret to avoid meta-strategizing. If you want to level as fast and as much as you can in story mode, visit every room, kill every mob, open every chest, and read every book. Max level is 15 and there's more than enough XP in story mode to get there without visiting every single level.
Magic XP is different and I know less about it. It seems that magic gains XP in a lot of the same ways, exploring new rooms, reading books, casting magic, but it also seems like your magic skills slowly train themselves passively too. I have no evidence of this but I suppose it would be pretty easy to test by leaving a character idle in a closet for a while and checking back a few hours later to see if their magic has leveled up.
Hope this helped
