I think this was answered in another thread. If memory serves, the first is how much power you can draw while the second is how carefully you can wield what power you have drawn. Or something.
Does this use of conviction and discipline just count for spells, or do true believers use them in the same way for their powers? The outline on the website mentioned that conviction was a must for them but didn't mention discipline.
In fluff terms, Dresden has maxed-out Conviction and Martin has maxed-out Discipline.