You have to get very low corruption before you will be able to advance.
You can do that by talking to Sen, the black goat farmer to the far northwest of the plains area where the tent is and helping him out. After that you just sleep in your tent.
I do not know why,but the purity is lock at 70.I had work for the goat many times,but the purity still lock at 70.This way is useless.However dressed or naked,work for goat has no effect at purity.
The things I can get from goat is just two bad endings.
