There is a dignity to developing virtue. This dignity comes from cooperating with grace. God can, in an instant, take away your craving for all fast food. That is a sovereign special grace. However, God seems to prefer to allow us to cooperate with that process.
"Everything is grace, don't question that for a moment. Some mysterious way God allows us to cooperate with that grace so we can say, 'God we did this together. You gave me the grace. It was all grace. But, I cooperated with it.'"