I'm not a big fan of the book. From what I understand, I think that Stephen's epiphany was more or less a gradual process. I think that the encounter with his dean had Stephen reconsidering some of his beliefs and his encounter with Temple finalized them in a way. His reasoning when debating with his friends becomes entirely based on art instead of religion as one would have assumed. I think this is an important transition. In order to truly understand something or to be able to say that you have examined all aspects of it, you need to think in a more artistic way. This gives you an entirely different perspective on things, just like Stephen displays. I think this will really make a difference in his judgement and beliefs later on in his life.