No single message, but a lot of important ones.
1) Don’t give up. Ever! No matter how bleak your situation may seem.
2) Have your work be something you love. By this I don’t mean anything fancy or something that will sound good at a party. In Vanderbilt’s case it was simple. He loved money. He was always thinking about (then doing) whatever it took to make money. That made hard tasks easy. As long as he had a good plan and the plan delivered.
3) Being fancy is what it is, strokes for your vanity, but it is window dressing. Vanderbilt was notoriously clumsy whenever he tried to show off for the swells (New York’s old money) but in the end it mattered little. He won what he deserved to win.
4) Make sure you have a mother that thinks you are fated to accomplish important things (Freud, FDR, Vanderbilt, unfortunately Hitler). Obviously this is not under the control of the reader. But he or she can always go back to message 1. “Don’t give up.”
5) In all seriousness, Commodore is loaded with messages. How could it not? Burch the reporter is interviewing a man who knows he doesn’t have much time left. He wants to figure out what it was all about. He’s got a lot of observations. He wants to make peace with his dead father, his dead wife. After he’s gone, he’s hoping things will work out as he has planned. Interestingly as he is dying his mind is totally alive, going over incidents, and over them, and then one more time. The message for the reader, get that stuff done so you can die in peace