Well my idea behind the cauldron would be with the mindset that the gods will not let just anyone into their little paradises simly because they claim to be devout. If they had not lived their lives to the standards of their gods then maybe they made an agreement with Beltine who takes on these unwanted souls. And should they serve their penance they may request Beltine scoop them out of the Cauldron and give them a second chance. 

Each god will still have power over their little domain, Beltine included. But she needs test subjects and the other gods may not be willing to take those into their palaces who they believe are unworthy. So they need to go somewhere.