The reason you are "helping" the magisters is to track down source.. the cook had source power and was worth investigating... even if you didnt get anything useful out of it.. your entire purpose in act 2 is tracking down source power no matter what you have to do.. even making deals with demons and undead just to gain that power... the human god at least sais "do whatever it takes"
So that is why you would be helping them.. because its a chance to learn more about source.
