[…] Love the cause. “Evangelist” isn’t a job title. It’s a way of life. It means that evangelists must love what they evangelize. No matter how great the person, if he doesn’t love the cause, he cannot be a good evangelist for it. If you don’t love it, don’t evangelize it. This has hiring implications too: a good education and relevant work experience are not sufficient. It’s just as important that an evangelist loves the product or service [or topic]. […]

Guy Kawasaki, first Technology Evangelist at Apple, in his blog about Evangelism