I seem to be on the short end of new ideas these days.
He says that discipleship is the process of learning to be a Christian (I'm paraphrasing). We sit at the feet of Christ, and learn how to live the life God would have us to live. Stewardship, on the other hand, is the next step. Once we have learned about Christianity, and how to follow God, we are called to use our gifts for the transformation of the world. It's the next step.