In the Temple enter the room with depicted hangman (you can make sure that you're entering the correct room by checking what your character say when he enters it). Use all three altars. The correct combination is:
Rephen, the blacksmith of destiny
Throughout the game you will come across different herbs that can be used to make potions. It is a good idea to pick them whenever you see them so that you won't have to look for them later.
It is suggested that you quicksave before drinking Soulgreep. Once you are in the Temple of Sacrifice there is no way out unless you are successful with the answers. If you are wrong... game over.