First, obviously it's the significance of an American winning Boston this year. I don't think he was even on the radar as a possible champ, but he knew he could do it. So he did.
For him personally, I think it's how far he came since NYC marathon this last fall. He had a really rough race and hardly finished. He ran with a semi-elite guy to the finish, and the guy wrote this beautiful story about it:
I watched his post-win interview while eating lunch at my desk and when they played the national anthem I was SO choked up- what an amazing story and a wonderful ambassador for the sport, and for the US- go Meb!
“No,” he said. “Today is not about us. It’s about representing New York. It’s about representing Boston. It’s about representing the USA and doing something positive for our sport. We will finish this race holding hands.”
Last year, Meb came and spoke to my marathon training group. He was so down to earth and funny (and also totally understood he was talking to a group of people semi-terrified of running their first marathon - and adjusted his talk accordingly). He really made a great impression on the crowd.