He came up with one purpose, which was to educate others about how the bone marrow donation process works, and how easy it is for people to do. But it became clear by the end that he still wasn't quite satisfied with that purpose. He was still struggling with the question, being willing to stay uncomfortable until he found some answers. And that was the beauty of it. I mean, just think about how much of our lives we spend plodding along, doing whatever we're doing without asking ourselves why.
Some people live their entire lives without ever asking why.
It's more comfortable that way. We don't have any responsibility for how or where our lives are going. But here's John, looking deep inside and really asking himself WHY he's on the trip. Now he's taking responsibility, and searching for the reason he chose to do the trip. He's not settling for the idea that the ride just happened to him.