Parrei is a gift from the gods. It is the power of devotion.
You have no control over how much parrei you get or what you can do with it — that is entirely at the discretion of the god or gods that you worship. And it’s only gods, plural, if you’re Light, because none of the other gods get along well enough to share.
Over half of all Light priests in the galaxy have parrei. Pretty much all Light priests who live and work on Light worlds have parrei. They all get one gift in particular: healing. Lots of people have converted to or stayed in the Light just for healing. It’s a rare thing to see someone die young in Light territory. Got an injury? Get it healed. Got an illness? Get it healed. A few seconds of prayer from the Light priest, and you’re fine. Other than deaths in battle, Light paths live long and healthy lives. The bastards.
The Light gods do give parrei beyond healing, but that’s much rarer. The Prophet and the councilors have other powers, powers that can be used offensively. Maybe some other Light priests can also do more than heal. I’ve never really looked. I don’t like the Light.
There are at least fifteen people in the Gray with parrei: the five Admirals, the five senators, and the five head priests. There might be a few people beyond that with parrei, but they keep a low profile. As for the abilities of Gray parreishi, even I’m not sure. I’ve never seen the Admirals or the senators use any weird powers. I don’t know about the head priests, since I don’t watch them. They’re even more annoying than the Light.
There are all kinds of crazy rumors about Death parreishi — that they can bring a newly dead person back to life, that they can speak with the dead, and that they can kill a person just by looking at them. I don’t believe any of that. The only reason there are so many rumors is that there are so few Death worshipers, let alone Death parreishi. There isn’t a Death lord, and that further fuels rumors about Death powers. The whole bringing a person back to life would make more sense for a Life parreishi anyway.
If you thought the Gray gods were stingy with their gifts, then strap in, because naturally the Dark is even worse. The three Dark lords have parrei, obviously, and a shit ton of it. Are there any mortal Dark paths with parrei? I don’t know, and I wouldn’t bet on it. If there are, they probably don’t live long, since the Dark loves in-fighting and the lords would feel threatened by such a person.
Just to be clear, there is no such thing as a Neutral parreishi or an Unattached parreishi or anything like that. Neutrals don’t worship properly, so obviously none of the gods are going to give them gifts of power. The Unattached perform a very important and very necessary function, which the gods encourage and appreciate, but that still isn’t enough for the gods to give power to the Unattacheds.